I have 89 F150 thats screaming, did this last summer and i changed the IAC motor. problem fixed, well just yesterday its back, was wondering if it went bad again? or is sumpin else wrong to cause this? thankz a million.
Could be alot of things,IAC or ABP (air bypass valve as ford calls it),or anything else.Look for vacuum leaks first,especially the throttle body or the ABP valve gasket.If it isn't something simple,it's worth it to have it properly "scanned" for codes to determine the problem,rather than making expensive guesses.You can also get a handheld code reader,or a code jumper,and read the codes yourself.If you need the code definitions let me know,as I'm an ex-ford electronics tech.