QuestionI own a 1991 Ford F 150 4x4 w/5.0L v8. The problem is only some sometimes on a cold start or even after driving it will lope in the idle. I can hear the tb gasp for air it recovers and repeats. Only after I drive it by 2 footing will it straiten out. So, I did a tune up new plugs, wires, cap %26 rotor along w/ oil change and pcv. Even installed new AIC valve. after the work it ran beautiful for 1 day then it started again. So, checked plugs, wires, cap & rotor and double checked AIC and everything is good. I tested the AIC before replacement and it was bad but now experiencing same symptoms. Any suggestions would be helpful. I do not have a scan tool so hopefully will have that done today at parts house since I am really tight on funding and they will do it for free.
Answerok. a hunting idle can be a few different things, the IAC being one common failure.
The others being:
vacuum leak= with engine idling , spray a small amount of carburetor cleaner or other combustible spray near and around intake. please wear safety goggles. if idle speed changes, look for source of the leak.. intake gasket leaks are common.
second: EGR= disconnect the vacuum hose leading to the egr valve and plug it. If idle quality improves, you have a problem with the EGR circuit.
third: You may have a slow or dead oxygen sensor. this may cause fuel response to be too slow, causing rising and falling idle speeds.
Unfortunately, the computers in these vehicle were not smart enough to pick up on these type of problems and point you to the affected area.
