High Idle on a 1988 P30 Carburated 454 (not choke)

[Flybynorth]

After the engine warms up completeley, it idles way to fast. when it is cold, you start it, it idles fast, you kick it after a couple minutes and it idles down to normal. The longer it runs, the faster it idles. I have fixed a bunch of vacuum leaks and replaced most of the vacuum line, a little stumped on this one. The choke actuatordoes hang occasionally but I recognize that which is a different probelm it appears than the one where theengine always idles fast after warm up no matter what. Idle screw backed down to less than zero throttle.

[kenwautoone]

Still think you have vacuum leak.try spraying a Little carb cleaner or brake clean at throttle shaft, than on base gasket under carb.might look at weights and springs in distributor.Pcv hose?.....ken

[EldoradoBill]

3 things...idle screws, (both fast idle cam and curb idle), vacuum leak, or advanced timing

[Rickf1985]

An IAC valve is on fuel injection only. It works hand in hand with the O2 sensor and MAP sensor to set the idle speed on OBD controlled injected engines.

[Flybynorth]

Finally found the problem.      The Secondary throttle plate was being held open ever so slightly by throttle plate shaft retaining pin. The pin was bent like a cotter pin and it was hitting a bolt on the intake manifold. Bizarre!!