ok my truck its a 98 f-150 with a 5.4 in it when the engine is runing it will under idel and over idel!!! sometimes it goes under 500 rpms and then sometimes it goes all the way to 2000-3000 rpms. it also does this while ur driveing it, like it will start to go faste with out u pressing the gas.

what would be makeing it do this???

 

I know that some F-150s have the wrong EGR installed. You should check that. Find out the right part number for truck from the parts dept.

 

Hey Peter, how do know that some f150 trucks have the wrong egr and which ones? What are the symptons? Thanks,
Terry

 

My 5.4 had a bad IAC valve. Dealer replaced and no problems.
(200.00 later though)