1994 460efi wont idle down - can anyone help - 460 Ford Forum
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post #1 of 55 (permalink) Old 01-10-2008, 01:42 AM Thread Starter
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1994 460efi wont idle down - can anyone help

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
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post #2 of 55 (permalink) Old 01-10-2008, 07:28 AM
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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...

SteveL

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post #3 of 55 (permalink) Old 01-10-2008, 12:36 PM
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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 )
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post #4 of 55 (permalink) Old 01-10-2008, 02:54 PM
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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.
Mark
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post #5 of 55 (permalink) Old 01-10-2008, 04:37 PM
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Quote:
Originally Posted by jc10000rpm
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...

SteveL

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post #6 of 55 (permalink) Old 01-10-2008, 09:21 PM
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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.

If they can get you asking the wrong questions, they don't have to worry about answers.
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post #7 of 55 (permalink) Old 01-11-2008, 12:51 AM Thread Starter
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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
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post #8 of 55 (permalink) Old 01-11-2008, 12:56 AM
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My 2c says ya got some sort of leak where the EGR was!

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post #9 of 55 (permalink) Old 01-11-2008, 01:00 AM
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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.

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post #10 of 55 (permalink) Old 01-11-2008, 01:00 AM Thread Starter
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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
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post #11 of 55 (permalink) Old 01-11-2008, 01:08 AM Thread Starter
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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....
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post #12 of 55 (permalink) Old 01-11-2008, 01:12 AM
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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.

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post #13 of 55 (permalink) Old 01-11-2008, 01:18 AM Thread Starter
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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....
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post #14 of 55 (permalink) Old 01-11-2008, 10:48 AM
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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!

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post #15 of 55 (permalink) Old 01-11-2008, 12:19 PM Thread Starter
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: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 ?
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