If anyone can diagnose this please help! My truck (97 F150, 5.4L auto, 132000mi.) will drive fine at highway speeds for approx. 20mins, then as soon as I get to the first stop, then try to accelerate again, it will not take throttle. It burbles, bucks, and diesels, and will basically only give me about 500 rpm increase, no matter the amount of throttle I give it. It will do this for about 5 seconds, then begin to run fine and accelerate. Vapor lock? Clogged fuel filter? I'm going to change the fuel filter this weekend, but I doubt that is the cause. I've also noticed a couple of times at idle, when the rpm will fall to about 300-400 and almost die, then it will return to normal idle after a couple of seconds. Not sure if this is related. No check engine lights. Any ideas? Thanks for any suggestions.

 

the idle and die is probably your iac, and i doubt its related. Pull it off and clean it with some brake cleen see if that helps. The other problem could be a couple thing, maybe the throttle posision sensor. Im not sure if that can account for the idling and near die situation but it might. The pcm might be detecting it erratically and thereby not using the iac properly but i dont know if those two parts actually connect to eachother in any sense.

Any ce light? that would be the most useful.