I have a '99 SD w/ the 5.4L V8 and when the truck is idling it is fine for a few seconds but then the motor sounds like it is about to cut off. Watching the tach. it shows the motor droping down to about 400-500 rpm's for a few seconds then jumping back to normal. What the hell is going on?

 

Misfire? Beats me, I'm no wrench head. Loose plug wire or something, I've run into that in the past doing similar rough idles.

 

Sounds like your IAC (Idle Air Control) valve needs to be cleaned.

 

Where is that located on my truck?

 

It's round and about 5" long, located on the L/H side of the throttle body. It has a single connector on it, and is held in place by two bolts. Easy to remove and clean.

 

Is this a common problem?

 

Yes, it's a rather common issue.

 

This valve allows air past the throttle body during idle. It is likely that this needs cleaned or replaced. If it almost stalls and then recovers, this valve might just be dirty.



Ooops, I am sorry, I should have read on. It is not allowing me to delete.