Am having problems with the 460, in my 1 ton van.It won't idle unless the curb idle speed screw is all the way in. Wants to die or idle poorly when I put it in gear. Idles fair when in park. Engine is in really good shape mechanically,and I found no vacuum leaks. I replaced the spark plugs & wires, new distributor cap and rotor. Rebuilt carburetor, done by a friend with 40 years Ford experience. Currently running it off a gas can, with a clean can and fresh gas. What should I try next? This is frustrating me!