Originally posted in the "chip" forum. My apologies for being new....

I bought my used '99, 4X4 lariat , about a month ago with 59K miles on it. First off.... I love the truck.
I've been having problems with the idle. My symptoms include an intermittent "bad" idle. Normally, when all is well, the idle jumps high for about 3 seconds.. then kicks back down to normal. (from the tach). When ornery, my idle kicks high and immediately falls to stall. This will persist until I continuously start it and/or brake drive it. Then all is fine. Does ANYONE know what this might be? The dealership is closed today (memorial day) and I'm p.o'd.
Throttle body? Sensor? ??

Thanks for your input, ahead of time.

 

There is a hose that goes to your throttle body that has a sensor on it. Not sure if it is a throttle position sensor or not. Anyhow start your truck up and open the hood and listen. You may here a hissing sound, and that is a small hole in that little hose. My mom's expedition did that and i found the leak. Replace the hose or otherwise seal it, and it went away. Don't know if that is the prob but its a place to start.

Good Luck.

 

I have and 00 SuperDuty with the 5.4L.. I had an IAC (Idle Air Control) valve go bad.. Truck would not idle.. It would start, goto 1500 rpms, then die, (unless I kept hitting the throttle)..

Once, I was able to drive it home, and by the time I reach my house, the problem was gone. but it returned the next morning..

Sounds exactly like your symptom.. Dealer replaced the IAC and all is well..