I have a '99 F150 with a 4.6, 101k miles. It has had the basic service performed (plugs, wires, fuel filter, etc.) It has developed an idle problem. Occasionally the idle speed will suddenly jump from 600-700 rpms to 2000-2500 rpms. There has not been a pattern to when this occurs. Sometimes it will do it when the truck is cranked and other times it will happen while driving it.
Generally cutting the truck off and restarting it makes the idle speed return to normal. It did this a few times about a month ago and then quit. Now the problem has returned. It has happened 3 times in the past 2 days. Other than when the idle speed jumps 'way' up the truck runs and idles perfect. The check engine light has never been on at any point. Thanks for any help.

 

I would look into the IAC (Idle Air Control). It is probably sticking. Quite common on higher mileage vehicles.
Jimmy

 

sy302: If the iac is not at fault you may want to look at the tps
throttle position sensor may be contaminated by improper throttle
bodie cleaning, this not to common but does happen when the
throttle bodieis cleaned by just drenching the bore of the bodie
& not keeping it away from the tps, the damage to the tps if it is damaged is permenant to the sensor. The most logical repair is to replace the old one & calibrate the new one.
keep us informed turbo ted

 

Thanks for the replies. The throttle body hasn't been cleaned so the TPS wouldn't have been damaged that way. That's not to say that it's not the problem. Would cleaning the IAC fix it or would it need to be replaced?

I'll most likely be trading/selling this truck in a couple of months and I don't feel like spending much $$$ on something that I'm not going to keep.

 

replace the iac. Cleaning it might work, but it will most likely come back within a few miles.

Its not a job that you want to do twice, so just replace the part the first time.