1994 460efi wont idle down - can anyone help [Archive] - 460 Ford Forum

: 1994 460efi wont idle down - can anyone help

01-10-2008, 01:42 AM
I have a 1994 f-350 w/ 460 efi .....the air pump and assoc plumbing has been taken off because it was all rotted and leaking and the egr has been plugged because the piping was rotted as well.... I now have a very quiet - but fast idling truck

I bought the truck to use off road as a plow/farm truck....it did idle down before I fixed (removed) all the exhaust leaks in the pollution plumbing....the vacuum lines for the pollution stuff are blanked off and I am getting 20 in vacuum gage - so I dont think I have a vacuum leak - dont even need the vacuum reservoir any more - heater works fine without it...

I advanced the initial timing to 14 degrees from the spec'd 10 degrees...seems to run real well....but cant idle down - if I retard timing it slows down but thats not what I want to do....

does anyone know enough about these efi engines to help me out?.....idle is probably about 12-1300 rpm --------not safe for a plow truck on ice/snow

01-10-2008, 07:28 AM
If you have a DVOM, check the voltage at the throttle position sensor,
should be under 1 VDC, also, pull the idle air control, plug the two holes,
start the truck, if it idles, then you either have a vacuum leak, or your
throttle blades are open too much. Clean the passage in the IAC, reinstall
and start again. Try these things first, and report back...

01-10-2008, 12:36 PM
just to add to the above post.....

sometimes carbon can build up enough on the throttle-body and cause the blades to stick open ( above the 1 volt level on tps )

01-10-2008, 02:54 PM
Replace the IAC motor that is the problem 9 times of 10 with EFI Fords whit the broblem you describe. Its the round thing with wires coming out of one end bolted to the throttle body to intake manifold adapter.

01-10-2008, 04:37 PM
just to add to the above post.....

sometimes carbon can build up enough on the throttle-body and cause the blades to stick open ( above the 1 volt level on tps )

That is true, if you decide to clean the throttle body, remove the TPS
and put it under your pillow, that way, it'll still work when you're done...

01-10-2008, 09:21 PM
Going through this right now with a 351w in a '94 truck. When I unplug the wire connector to the Idle Air Control valve, it idles down correctly, but runs rich. I found that my throttle position sensor is showing a constant 3.6V no matter what position the throttle is. One wire is ground, one should be 5v constant, and the other should swing from less than 1v to 5v from closed to open throttle. If idle goes down when you unplug the IAC valve, look to replacing the throttle position sensor.

01-11-2008, 12:51 AM
havent used my DVOM in a while - found the battery dead - will get one tomorrow - need a procedure for testing this under 1 volt voltage at the TPS.... WHERE am I testing for this under 1 volt?...with the plug plugged into the TPS I assume...or unplugged? & which pin is supposed to have the 1 volt or less?????...what are the OTHER two pins????

I unplugged the IAC and the engine ran about the same (still fast)....then took the IAC off the engine and plugged the two holes - seems there is only heavy vacuum on the rear hole and none on the front one - but non the less.....STILL ran fast with them plugged.....rear hole was HUGE vacuum leak - would have killed engine w/o plug...sprayed some carb cleaner into IAC and put back on engine

I did get it to idle down with everything hooked up by putting a heavy sheet of cardboard over both the throttlebody inlets - full coverage...the vacuum sucked the cardboard tight to the throttlebody - engine started to run slow enough to stall - punched a small hole in the cardboard and it ran perfect....a nice idle - just like Im looking for - Im thinking maybe the throttle plates ARE hanging up - will get some throttle body cleaner - is there a procedure for this that is preferred....or do I just spray into the throttle body - like carb cleaner?....while running or when off ?

appreciate some guidance on this.....thanks

01-11-2008, 12:56 AM
My 2c says ya got some sort of leak where the EGR was!


01-11-2008, 01:00 AM
Not trying to be smart but have you tried setting the timing back to 10 degrees and see what the idle is before you go start guessing at everything else.

01-11-2008, 01:00 AM
forgot to mention - I took the truck for a first ride today (since putting engine back in) around a long block - I kicked it in the *** at about 10-15 mph and the rear tires lit up - left about 10 feet posi & then I got out of it...it does start/run/drive nice....just the fast idle issue problem....Im like'in the 460 and those 4.30 gears about now......

hope to get instructions asked for in previous post - thanks

01-11-2008, 01:08 AM
the EGR is left intact - along with all the original hoses/solinoids etc....JUST the pipe from the exhaust manifold disconnected.....and that was brazed closed - so leak

I sprayed starting fluid (either) around the base of the "cobra head" throttle body manifold thinking a leak would draw it in and engine speed would pick up....it didnt....but shot a little in the throttle body opening and it didnt increase speed there either...so maybe its ALREADY idling too fast for that test to work....

01-11-2008, 01:12 AM
Brake booster hose, PVC hose, or even the brake booster itself can be sources of large vacuum leaks that will cause a much higher idle. On the TPS, there should be 3 wires. One will be ground, one will be 5v (with key on), and other (I think the middle one on the harness) is supposed to go from less than 1v at closed throttle to at or close to 5v with throttle all the way open.

01-11-2008, 01:18 AM
after reading your replies - wanted to mention there was no change unplugging the TPS

I really dont want to go back and set the initial timing back to 10 degrees - unless there is no other way to reduce idle speed - there MUST be - never heard of an engine where you cant adjust the timing a bit

there must be too much air getting past the throttle plates - because the idle was actually SWEET with the cardboard with a small hole punched in it placed full coverage over the throttle body inlets....

01-11-2008, 10:48 AM
vacuum leak!!!!!!! it wont idle down. or the throttle is hanging open!start it up and start spraying everything it carb clean till you find your vacuum leak!

01-11-2008, 12:19 PM
:idea: spraying around DOESNT WORK!!!!!!!!!!!!!!...its already running too fast - even sprayed directly into throttlebody and no real change - so lets put that one to rest

will unplug the brake booster and recheck the pvc and all the vacuum lines

Im thinking the computer somehow doesnt like the air pump and assoc plumbing gone and the egr SUPPLY PIPE blanked off (didnt remove egr-or any assoc solinoids/hoses)

anyone know enough on workings of ECCIV to "fool" the computer into thinking all is well ?

01-11-2008, 12:48 PM
Yes it is throwing codes. It is commanding the EGR valve to move but since its disconnected it is not moving. There is a position sensor on the back of the EGR and it is seeing no movement. I would suggest that you reconnect the EGR as it does not hurt performance but does help gas mileage. Also I think the computer does not like the fact that you moved the timing as well. The fault light should be on.

I suggest you slow down and take some time to read this site. Speed Density OEM EFI system are not too forgiving when it comes to making changes in what the factory designed.

01-11-2008, 03:12 PM
If that don't work, you could try pulling the intake to see if there's a buggered intake gasket causing a vacuum leak.

01-11-2008, 07:25 PM
You still dident check the IAC. Im a fleet tech. and when a EFI Ford idles too high Im betting on the IAC being bad. The IAC (or idle air control motor) controls the idle by bypassing air aroud the throttle plates just like a controled vacuume leak except in this case its not being controled.

01-11-2008, 07:45 PM
The IAC valve allows air from the front hole to go into the back hole. If the back hole was plugged and it still idled high, it's not the IAC valve. He said he did that and it still idles high.

01-11-2008, 08:38 PM
What I see not mentioned and what was mentioned was this ......
it idles just fine with a small hole in the cardboard..........
Is the intake hoses connected and are the air horns still in the pipe????
Unsure if there are airhorns on the 94 with mass air ?,but its not going to like having the hose unhooked and no signal to the mass air sensor either....

The factory system as mentioned does not like change ,hook the egr back up or you will encouter a lean condition as the engine is calibrated for the extra gas in the egr.Its also needs the oxegen sensors,I have also heard of problems with the factory set up and no cats ,I am unsure of what this would cause ,but have heard it mentioned before.
I know the 94 is mass air ,I have never liked those sensors ,seems everytime a mass air car runs bad its that thing,there pretty sensetive items.
There sensetive enuff for me to wonder how they would do in a plowing impact type of enviroment....?
The timing is at a set number because the computer is set to calculate other factors based on this info .You can fool with it some ,but the computer will try to compensate for the adjustment as the computer concludes it must be out of adjustment and tries to compensate for it being out of spec,best bet is to set it at factory specs.
Did you change the cam ?,if its not mass air ,it will not like anything different than the factory specs or really really close.....if it is mass air it will accept a little bigger cam than the speed density set up,but very much bigger or smaller for that matter,will not work well.
Just some info for thought.

01-11-2008, 09:10 PM
I concur, the air is coming from somewhere.

Did you remove and reinstall the IAC? If so, did you install it correctly, or did you reverse it? The input and output sides do matter, the device is a spring assisted solenoid and airflow direction plays a role on how the valve operates.

When you messed around with the emissions plumbing, what did you do about the fresh air line that runs to the exhaust? Is this sealed up? If not, a lean oxygen sensor reading can cause fuel enrichment, which will also cause a high idle provided the enrichment isn't enough to load the engine up excessively.

With an idle that high, you probably have a vacuum leak at least the size of a pencil lead, if not larger. Check all the gasket surfaces between the intake ports and the throttle body. Check the injector o-rings, the bottom ones. If one of those is missing or has rotted out, it'll draw air through the opening. Check all the vacuum lines under and on the intake manifold. If you've removed the thermactor controls, what did you do about the thermactor vacuum lines? Are you sure you don't have a 1/4" nipple on the back of the manifold somewhere that fed the thermactor control solenoids? It's easy to miss. Are you sure the vacuum line that went to the thermactor control solenoids isn't unplugged and laying in the fender well somewhere?

John I.
01-11-2008, 11:48 PM
I had a 1989 F150 that was doing the same thing. It had headers, and when the previous owener installed them, he disconnected the EGR. It would rev like crazy, and it would go even higher when I pulled it into gear. I put up with it for 2 years, tried swapping out tps, map, iac etc, and finally built a tube down to the headers, drilled a hole in the #1 pipe and re-connected everything, and it idled normally. I sold it the next day... :cry:

01-12-2008, 01:02 AM
My first thought when he said "and I put the cardboard over the the throttle bodies" was , it came burning out the exaust was going to be next statement ..!!! :)

01-12-2008, 10:05 AM
I advanced the initial timing to 14 degrees from the spec'd 10 degrees...seems to run real well....but cant idle down - if I retard timing it slows down but thats not what I want to do....

When you advanced the timing did you remove the spout connector before you moved the distributor? I know that's the only correct way to advance the timing on the EEC systems. I could be wrong on this so if I'm wrong someone correct me.

It's been a long time since I've had to work on my 94. I've since sold it for an oil burner.

01-12-2008, 11:43 AM
I set the timing per factory procedure - disconnecting spout connector - have seen a few guys on this site say they have advanced the timing to 14-15 degrees with speed density (which this is) with good results....

I bought this truck almost a year ago and drove it only about 20 miles home.....my recollection is a bit foggy - I must admit - dont have 20/20 recollection of how it idled - dont remember it with high idle though...it had other issues though that might have distacted me like leaking exhaust manifolds both sides ( six broken exhaust bolts - leaked so bad the heater box melted ) and some pollution tubing leaks...the PO used boltcutters on the EGR supply tube (a real artist)

After cking compression - finding good -I took the engine out and ground the crank and installed new bearings which it needed badly and all new gaskets (felpro) ....dont have any oil leaks....sprayed starting fluid around manifold and no indication of vacuum leak - have 20 in Hg reading on vacuum gauge (steady)...I know where the vacuum ports are on the engine....they are all hooked up with good (some replaced) hoses.....the thermactor tube to exhaust was eliminated by PO when he installed new system - removed all the thermactor hoses/valves tubing and plugged all the exhaust recirc - but left the egr and ALL the control solenoids in place....just put a softplug in egr exhaust supply tube and brazed in place....the engine is very sanitary looking now _ I am going to disconnect the brake booster and see if maybe it has an internal leak next time I get out to the garage....

when I removed the IAC wire it made no difference - when I removed the IAC from the engine - there was VERY heavy vacuum from rear port and NO vacuum from front port ---I blanked both and started - no difference...the inside of the IAC looked clean - gave it a spray of carb cleaner anyway....reinstalled - no difference

removed the tps and made no difference....I still have to get a battery for my multi meter to ck it though....a Ford tech at the local dealer told me probably not the problem - actually GAVE me an almost full can of ford throttlebody cleaner spray and told me he thinks throttle plates are not closing all the way - have to spray - will report findings

am not seeing check engine light - did flash for a brief second or two - when I got on it and did burnout & then got out of it - then light went right off and stayed off....

this engine runs MUCH better than when I got it - I replaced the O2 sensor because the tailpipe was coated with soot from running rich when I bought it - now clean as a hounds tooth...and it has a lot of grunt (running empty) - actually quite impressive for a big truck ( I like the way it grabs Rs with those 4.30s....Im an old hot rodder).....snow is supposed to be coming next week...guess Ill see JUST how much it has when pushing its 9 foot blade....

this is an off road truck that I NEVER expected to put anywhere near this kind of of work/time into.....the "might as well" syndrome got the best of me ....the fast idle is the only bug-a boo left - Im hoping the spray does the trick - will let everyone know.....

thank you all for your help & keep it coming - if you think of anything new....

01-13-2008, 01:11 PM
all fixed -
there cant be a vacuum leak - spent enough time and a can of carb cleaner spraying/looking -----nothing - so after using some throttle body cleaner and still not getting slower idle decided to plug the holes in the throttle plates with small HVAC ducting screws - VIOLA !----------runs absolutely perfect now - a really sweet idle........with all the polution stuff off/plugged - I have no idea what kind of wrestling match the computer was having with things - but thought Id share what I found - hillybilly fix - yes - but it worked and I can

I still dont understand the IAC and the way its supposed to work.....when I disconnect the hose going from intake to the fitting on the bottom of that thing with the air horns in the middle of the intake tubing - there is no suction at the intake - until I rev it up - I thought the IAC was supposed to open at idle speed to provide air to idle properly -----this seems opposite - why would it open when throttle plates are open and engine is revving???

01-13-2008, 01:44 PM
What is your ignition timing at idle with everything connected?

01-13-2008, 03:06 PM
Are the throttle blades open too far? Was the throttle screw messed with at all? The IAC is a plunger type valve. On one side (the front) is a hole that goes to the air intake pipe. This is filtered fresh air that hasn't gotten to the throttle blades yet. On the other side of the plunger is the hole that is open to the intake plenum after the throttle blades. So the further the plunger valve is opened by the computer, the more air is allowed to bypass the throttle blades and go straight into the engine.

01-13-2008, 03:59 PM
after reading the response(s) I repeat
I still dont understand the IAC and the way its supposed to work.....when I disconnect the hose going from intake to the fitting on the bottom of that thing with the air horns in the middle of the intake tubing - there is no suction at the intake - until I rev it up - openI thought the IAC was supposed to at idle speed to provide air to idle properly -----this seems opposite - why would it open when throttle plates are open and engine is revving???

WHY is it necessary or DESIREABLE to bypass the throttle blades???...also again - isnt the way mine is operating BACKWARDS????- why bypass the throttle blades when they are open and IAC is closed (doing nothing) when at idle----------

STILL - I have to wonder WHERE is the air coming from at idle that makes it run fast & especially when I put the cardboard over the throttlebody -WHY DOESNT THE ENGINE STALL????.....my intuition would tell me there is a vacuum leak - like many of the guys that responded.......but after exhaustively looking and spraying ether and carb cleaner - Ive not found a vacuum leak that makes the idle pick up from sucking in the spray.....Im just confounded - the air necessary to run the engine is coming from somewhere.....I was grasping at straws when I decided to put the screws in the throttle plate bleed holes - Im thankful it slowed the idle - but my natural curiosity would like to know whats going on here?

01-13-2008, 04:27 PM
One of those rare places to get a vacuum leak is the brake booster. Not in the engine compartment, but behind the brake pedal where the rod goes from the pedal to the booster. Try spraying there and see if that shows anything. But if you pulled the booster vacuum hose and plugged it and it still idled high, I don't know from where the leak would be. I'm not familiar with the 460 IAC, I've just seen the IAC valves on mustangs, broncoIIs, and small block trucks. Those are all the same, with no hose attached to them, just a two wire harness. It's desirable to bypass the throttle blades because it's easier to have a solenoid valve than to try to rig up something to pull open the throttle blades directly in order to get enough airflow to keep the idle at the right rpm. TBI systems typically used a plunger type solenoid to actually open the throttle for idle control. I guess what I would do is plug off all vacuum lines on the intake and then if it idles correctly, hook up one at a time to see which one is the leaker.

01-13-2008, 05:24 PM
If your idle speed is already faster than desired, the IAC will close trying to slow the engine down. When you open the throttle the pcm pre-positions it for the next time you close the throttle. When your overspeeding at idle, spark should also should be running somewhat retarded trying to lower rpm. If thats true, that would indicate that your tps is functioning. Because you throttle body has holes in the throttle plate, when you have the t-body off the manifold and look at the throttle bores with the plates closed you should see no light around the plate edges. If you see light, the throttle set screw needs to be adjusted to close the throttle plates further. There should have been coating (orginally green) on throttle plates so that plates could be closed and not stick in the bores.

01-13-2008, 09:32 PM
I thought the IAC was supposed to at idle speed to provide air to idle properly -----this seems opposite - why would it open when throttle plates are open and engine is revving???

The path of least resistance, when the throttle blades are open, you will
have vacuum at both ports, mainly because there is vacuum on both sides
of the throttle blades as the plumbing from the air filter box is a restriction.
Even without the plumbing connected, you'll have vacuum on both sides
of the throttle blades, there will be less on the engine side, and more on
the filter side compared to the throttle being closed...

WHY is it necessary or DESIREABLE to bypass the throttle blades???...also again - isnt the way mine is operating BACKWARDS????- why bypass the throttle blades when they are open and IAC is closed (doing nothing) when at idle----------

The IAC is a valve, it allows more or less air to enter the engine depending
on demand. If your AC is working, when the compressor kicks on, the
idle may fall low enough to stall the engine, it needs more air, the IAC will
open and supply the air, the ECU will inject more fuel, the timing will be
adjusted accordingly. It's also used for cold start, the engine should idle at
about 1500rpm then as the engine warms up, the IAC reduces the idle rpm,
the ECU reduces the fuel, and timing is adjusted accordingly...

01-13-2008, 11:15 PM
canzus - your last paragraph peaked my interest in where exactly the temp sender is located - the one that controls cold idle and sends engine temp to the computer.....MAYBE mine is sending the computer a signal - telling it the engine is cold - even after it warms up-----is there a test procedure to test it?

would love to fix this thing right - Im not a jerry rig kind of guy - but I needed it to slow down & I did what worked -even if its temporary

if its on cold engine warmup mode - its probably open loop - in which case Im not gonna get any kind of fuel efficiency - a reason in itself to fix right

since I replaced the o2 sensor the tailpipe is clean - not caked up with soot like before - I thought that meant I was im in closed loop-----is there a definitive way to tell that engine is going into closed loop?- what is it?

I DID pull the brake booster vacuum hose and held my finger over it - no change in rpm - I figured no vacuum leak there - so booster OK

01-13-2008, 11:29 PM
use propane to test for vacuum leaks! i use the small cans with a torch head but cut off the head of the torch and add a hose to it! turnit on and run it around everything, even sticking it in the valve cover checking for vacuum leaks into the crank case! propane will make the engine stumble!

could have sucked the intake gasket into the valley area! just a thought!

is the throttle sticking open at all? i keep thinking you have a vacuum leak where the egr and or air system was removed!

01-14-2008, 01:59 AM
is the throttle sticking open at all? i keep thinking you have a vacuum leak where the egr and or air system was removed!

the throttle plates are NOT sticking and are now squeeky clean after being cleaned with TB cleaner

the egr WAS NOT REMOVED- the supply pipe was just plugged & the thermactor air injection system had a simple vacuum line to the valve located on the pass side valve cover - which is now plugged...the rest of the thermactor system was exhaust related and is also plugged


Im going to explore the manifold and coolant temp sensors possibly not working - I wish someone could tell me how to test them and how to know for sure that the engine is in closed loop

01-14-2008, 02:06 AM
practically impossible that intake gaskets could get sucked into the valley ...there are six studs - 3 on ea side that hold the gaskets -when the manifold is put in place and when the studs and the rest of the fasteners are tightened -also i sprayed copious amounts of carb cleaner on them - with no results...can actually see the gaskets & theyre fine

01-14-2008, 06:57 AM
How about a bad pcv valve or the wrong one...its kinda already a calculated vacume leak,what if its not "calculated"and is an open port?

01-14-2008, 10:23 AM
Hello,although I have been reading this forum since network 54 this is my first post.I'm a automotive repair shop owner and have been turning wrench's since 1978 ,so with that said I might be able to help you out.On the bottom side of the intake gasket where you cannot see I've seen the gasket either torn or a small piece sucked in the port.After reading everything that you've done or tried I would highly suspect this to be the problem.Hope this helps.

01-14-2008, 10:42 AM
Yep, it does happen even on the big block fords where the bottom of the intake gaskets get sucked into the port. I'd really be suspect of that, especially if the surface of the heads were machined at all.

01-14-2008, 01:55 PM
Yep, it does happen even on the big block fords where the bottom of the intake gaskets get sucked into the port. I'd really be suspect of that, especially if the surface of the heads were machined at all.

exactly my point! i have seen this happen on many of cars not just BBF's!

and if nothing up top is leaking then i am highly thinking its the lower half of the intake sucked in!

01-14-2008, 01:57 PM
practically impossible that intake gaskets could get sucked into the valley ...there are six studs - 3 on ea side that hold the gaskets -when the manifold is put in place and when the studs and the rest of the fasteners are tightened -also i sprayed copious amounts of carb cleaner on them - with no results...can actually see the gaskets & theyre fine

how do you see the bottom of them thats in the intake valley? :roll:

01-16-2008, 09:47 PM
this isnt rocket sience guys...if I was very unlucky - (I dont think so) and brand new felpro gaskets somehow decided to get sucked into the intake port - THERE IS GONNA BE VACUUM in the engine - pan/lifter gallery /rocker areas of heads...Ill ck again but Im betting the computer is wrestling for control

If I have the type vacuum leak described here Id be sucking oil and burning it - like a bad modulator on a transmission....true?

01-16-2008, 10:20 PM
Fel pro gaskets are the ones known for sucking into the intake ports on these big blocks. Not saying that's definately it, but when all else checks out, that's where I'd look. As for sucking in oil and burning it, it probably would some, but not as much as you might think. The bottom of the intake ports are quite a ways away from oil and not much gets flung up there for it to be sucked in. If you could back off all the intake rockers and seal off the crank case and valve covers you could maybe somehow put some light pressure in there and see if it comes out the throttle.

01-16-2008, 11:03 PM
that or the IAC valve is on backasswards. which can be done on some fords. ive seen that as well. but i think someone mentioned it already!

and no it wont suck alot of oil in! but when mine did it, it sucked so hard on the crankcase, it would keep the oil fill cap on the valve cover(normally it would just fall off ) in the unlocked position. :lol:

and mine didnt smoke.

you covering the throttle body is what is making me think it sucked the gaskets in.

and just to add, you are removing the timing plug when setting the timing correct? have you tryyed setting it back to 10 and see where the idle is? some of these computer controled systems dont like it when you mess with the timing more the a degree or two!

01-17-2008, 11:44 AM
Or you used RTV that skinned or had a lump in it prior to getting the intake seated, and there's a teeny weenie gap somewhere causing a vacuum leak. I've done this personally several times; I'm simply too slow about getting the intake seated so I've switched to RTV Gray and I let it cure overnight before firing the engine. I'd rather have a gooey mess for a longer time, then have a leak.

01-17-2008, 12:45 PM
if the intake gaskets seal right - there shouldnt be any vacuum to leak from the "china walls" that are sealed with rtv...I have no oil leaks at all and sprayed carb cleaner and ether around the manifold /throttlebody/cobrahead manifold top - profusely with no change in idle

Ill ck for vacuum inside the engine by taking off the oil filler cap and putting my palm over the opening - if there is vacuum Ill know I have an internal vacuum leak - dont think Ill find one though - although I wasnt LOOKING I didnt notice anything when I topped off the oil -while it was running...

weather permitting - next time I get in the garage Im going to back the timing back to stock 10* and see what happens - my gut tells me the computer is doing this.....perhaps because of feedback(s) from sensors that indicate the erg is not getting any exhaust gas supply OR because the thermactor system is completely gone -

If I had a vacuum leak I would think the o2 sensor would heavy up on fuel and I would have sooty exhaust pipes and rich smelling exhaust....I have NO soot - no black on finger rubbed in exhaust pipe at all....and exhaust doesnt smell rich at all either

Im trying to have an open mind here - but the notion of the intake gaskets being sucked in the ports - under the manifold - where I cant see is something Im having trouble with - I cleaned the head and manifold surfaces with a 3m disc on a die grinder (gently/carefully) & then MEK and placed the gaskets on the heads (over the vertical manifold studs)- the ports matched up very nicely - put a appropriate amount of ultra black rtv on china walls and immediately placed manifold on engine.....torqued manifold in 3 steps in proper pattern and didnt start the engine for more than 2 weeks.....

appreciate you sticking with me - will report what I find/do...Im not a guy who generally likes to not understand WHY - and pride myself for having all my engines run the best they can - kind of HAD to hack this by putting the sheet metal screws in throttle plate bleed screws because it snowed and I needed the truck - really would like to get this fixed right - I m reading about the ECCIV on the net - hope to come up with answer by staying on it ....

01-17-2008, 02:34 PM
The adaptive capabilities of the EFI system will correct the air/fuel ratio up to 25% if necessary; to compensate for a vacuum leak. This can result in high idle and perfect air fuel ratio at the same time.

RTV can skin before the manifold is set down causing a leak. Whether the leak is through to an intake port or through to the crankcase, in a closed-crankcase OEM efi system, it's still a vacuum leak. All air must be metered. If air enters anywhere; even into the crankcase; it's a leak because the air eventually enters the engine through the PCV valve at closed throttle. A hole the size of a pencil lead is a tremendous leak at idle.

01-17-2008, 02:38 PM
The adaptive capabilities of the EFI system will correct the air/fuel ratio up to 25% if necessary; to compensate for a vacuum leak. This can result in high idle and perfect air fuel ratio at the same time.

just about to post that. :lol:
and btw the egr doesnt open at a idle. if it does it would run like crap and have a low idle.

and what are you talking about cobra manifold?

01-18-2008, 02:58 AM
Byronrace- WHAT?....rtv is gonna skin over before I put the manifold down??????? - what in like 3 minutes?...whats the alternative - if thats the case.....?

there is no leak - I sprayed ether and carb cleaner on the rtv end seals and no leak indicated

the cobra head is what local ford mechanics call the upper intake and throttlebody...it DOES resemble a cobra - if you look at it from the front.....
I sprayed ether and carb cleaner around throttle body and upper to lower manifold seam - no issue found

report of what I found today...as a check for intake gaskets leaking - I disconnected the pvc vacuum hose and plugged it then plugged breather on oil fill "spout" on valve cover - placed my palm tightly over the oil fill and felt or heard no vacuum ....when I re attached the vacuum to pvc - THEN there was vacuum at the oil fill - believe this to be normal.....also sprayed a shot of ether into the fill with pvc hose off and idle didnt change a bit

I backed the initial timing back to spec'd 10* from previous 14* setting...idle DID slow down quite a bit - I then put back the previously used sheetmetal screws back in the throttle body bleeder holes....and its right where I want it to be - idles smooth and reasonable speed ( estimate 700 rpm)...good manners when I shift into gear....

I dont like using the sheetmetal screws to hack a fix but -I think Im done with this - at least for now - unless someone comes up with something new ...I really dont think I have a vacuum leak - I think the computer is causing the high speed idle because of the egr supply blanked off and thermactor system gone- gonna go back and see the ford garage mechanics and see what they think

the one thing I notice with this engine is it burns gas like its going out of style....ran out of gas again today while testing/adjusting...Ill bet all told I didnt run it over an hour and a half - MAX - since it last ran out and I put 5 gallons in - mostly fiddling with the timing/idle /testing etc.....and moving in and out of the garage a few times - NO driving....I was sure spoiled with my old IDI 7.3 - compared to this - the old truck was nuclear powered

thanks guys....

01-18-2008, 09:45 AM
Hmmm, sounds like you don't have a huge vacuum leak under the intake at least. It must be running rich if you're sucking the gas down like that or you have a fuel leak somewhere. Did you check the throttle position sensor resistance? I just replaced the one on my 5.8L '94 truck two days ago and it completely fixed the high idle and sucking-the-gas-down symptoms. On that engine, there's 3 wires coming out of the sensor, black, green, and orange. Orange should have 5 volts constant when the key is on. Green is the one you want to check as it should swing smoothly from less than 1v to 5v with the key on as you open the throttle from closed to all open. Mine held steady at 3.6v all the way through the swing and a new sensor was $37 at Napa. Yeah, these issues can be pesky, especially with OBD-I. It's like the computer isn't really smart enough to tell you much of what's wrong, but there's plenty of little things to cause problems. As for the intake RTV, I've always let it set up a little before putting on the intake because it makes for less clean up when I pull it off. So even if it did skim in the couple minutes, I don't think that should be an issue.

01-18-2008, 01:54 PM
I hate to sound bad ,but it sounds like you are just shooting in the dark with alot of maybes......
There are proven technics for determining a problem ..
1 Use a vacuume guage ,it works
2 Use a code reader ,it works
3 You have a complete system with pieces missing ,no system without all the parts working ,so basically you have half a non working system

4 did you test or replace the injectors..........

A leaky injector will cause the engine to raise the idle to maintain fuel ratio
A vaccume guage will tell immediatly if there is a vac leak ..anywhere
A code reader will tell if any sensors are bad or not properly functioning and it also does a injector balance test.
I would goto the junk yard and retrieve the missing pieces ,so I had a complete funtioning emmisions system.

Those steps will get the problem solved,hope you do not wash the rings out or burn a hole in a piston ,while you pokin and hoping....... :o

Here is a very good article on vac guages and how to read them properly

Most auto stores will "lend" you a code reader ,such as auto zone.
I would imagine there is some one on this site who has almost all of the emmissions stuff for that engine and would be glad to see it leave the garage.
In all honesty ,consider the injectors junk , would you exspect a carb to hold tune for 100,000 miles ...? There has got to be wear and lots of it on the pintle of the injectors or atleast a little leak down or sumthing on atleast one of em and thats all it takes,at 200 bucks for a factory set ,it just makes sense to change them in a rebuild,alot of people differ on the injector wear ,but they do wear out at some point.

I can also assure you that motor should almost suck your arm up in that corbra head if you were to get it covered with your hand,it scared me just covering one side with my hand,I had visions of the rescue cutting my arm outa the intake.. :roll:

01-19-2008, 12:49 PM
shawnlee - you must have been speed reading and skipped over the couple time I said I took a vacuum reading and it was 20in Hg

appreciate all inputs - and dont want to offend anyone - but suggestions to spend large BIG money - because everything is junk is frankly annoying.........and doesnt help a bit - there isnt anyone on this planet that would spend what you suggested shawnlee -

the engine runs smooth and there isnt any rich exhaust or black sparkplugs - so I ll bet the injectors are just fine

I didnt expect a seamless transition from stock to all pollution removed - but the fast idle IS strange - now - with the throttle plate bleeder holes plugged with screws - I can stall the engine when I cover up the inlet to the throttlebody....maybe with it revving - it sucked soooo hard that it got enough air past the cardboard used to blank off throttlebody to not stall

I still think the computer is wrestling for control & dont really understand ...but it does run nice now & Im not wasting any more time or gas fooling with it until I have a better understanding of whatever Im about to do - will impact the way it runs and WHY......

Im gonna ck the spare tank/tank selection valve......maybe the return is sending the fuel to the other tank - I dont believe a 460 can physically BURN 5 gallons an hour in a driveway at high idle

thanks all who contributed.....but until spring or summer - Im done looking at this - there is snow to plow - cant wait to see how much gas that uses :roll:

01-19-2008, 05:29 PM
All I was suggesting ,is that using those tactics will lead to a answer or at least determine if its mechanical related and help narrow it down to the actuall problem.
It may be electrical/computer ,but one of the good scanners will show failure in that system or sensor........
The article on vac that I posted shows many many many uses for a vac guage to help track down or eliminate problems .
The parts you mentioned were missing should run about 50 to 100 bucks with shipping ,used.
Alot of people use this motor in a performance application and discard the emmisions components in the trash.
There are ways to determine if the injectors are really bad ,but the time/money and hassle usually costs about half the cost of good quality stock injectors,if one of the tests actually point to a few bad injectors ,not just start replacing things,thats rediculous. :roll:
I think it "may" cost more in long run in gas and damaged engine parts, than what I have suggested .....??????
I might be completely off base ,I am not the most exsperianced person there is ,but i try to be correct in what little help I am able to provide.

01-19-2008, 06:41 PM
Good luck man.

01-19-2008, 06:46 PM
those are bad about the pressure regulator going bad and forcing fuel pressure realy high.. hence dumping fuel at a alarming rate. and it is rather hard to diag something over the enternet.

good luck