Can someone let me know how you can tell whether or not your IAC valve needs cleaning (or replacing)? I have a '79 Ford F150 and when starting, I need to let the truck warm up a bit before I take off. Otherwise it stalls right when I put it in gear, yet starts right back up again. It's fine once I drive and doesn't stall at lights or any other stops. If I only make a quick stop and start it back up it doesn't require warm up however if I let it sit overnight or even a few hours, it requires the warm up again. It idles pretty rough when stopped at lights though, and revs pretty high.

I thought I'd try cleaning it at first to see how that goes and to save some $$. Any other thoughts?

 

I just had the exact symptoms on my 99. Once started and running, it drove ok until It sat overnight. The next day it would stall after starting until warmed up again. I changed out the IAC with an aftermarket unit from advance auto (BWD part) and now it idles well after a cold start.

Most of what I read indicated it was the IAC if stalling only occurred during a cold start. While the IAC worked for me, other likely causes for the 99 engine were vacuum lines or a damaged pcv hose.