I have a 1992 F-150 with 5.0 V8 I have this problem with it surging when it comes out of hi idle would this have anything to do with the IAC valve or something else one of my friends had mentioned that it maybe something like and air bypass valve is there such a thing or is it the same as the IAC. Well if anyone has anyideas please get back to me this one of my work trucks and I dont have to let it set at a garage so please get back to me asap

Thanks
Nick

 

I have a '89 4.9L-6 that has a similar problem. The RPM's will fluctuate to a high idle to almost stalling for about 10-20 seconds after startup. Also if I engine-brake down a steep hill, it will often repeat this behavior or stall when I depress the clutch to stop at the bottom of the hill. Any thoughts/suggestions?

 

Nick, IAC is a possibility. You can remove it and clean all the carbon build up out. Another think to look out for is vacuum leaks. By the way, Idle air bypass is the same as IAC...among many other names for it.

 

I have had this situation on various fords, and the easiest fix I ever had for it was cleaning/ replacing battery terminals. Didn't work every time, BUT DID work.Don't know or care why, but it's a cheap & easy attempt.