well, i have a 99 f250 sd 5.4L, and it had a rough idle at times, so i changed the spark plugs out to bosch platinum plugs. well, i never checked the gapping, and i heard a lot of bad about the bosch plugs in a mod engine. so, today i changed back to a set of new motorcraft plugs. then i cleaned the iac, and the throttle body. well, it seems to idle a bit smoother, but sometimes when i start it, it seems to act real wierd. it will idle from 300-800 rpm's, and wants to die. if i hit the gas, it will respond and then assume a normal idle. could this just be a bad iac, or something else before i spend the money on the iac. thanks !!!!

 

Yes, it could be the IAC. But no guarantees. An idle learn might help. Try disconnecting the battery, hit the brake lights for a minute, just to gently pull any juice from the computer. Then it will relearn over the next day or two.

 

great, thanks for the idea ! i will try it tonight and see how it acts for the next day or so !