I have a 2001 with 197k on it. Initially, on a cold start, it fires up and idles just fine. After a little heat has gotten in the motor, it starts to whine at idle like it might have a vacuum leak. It goes away when I'm on the throttle but returns the second I come off the throttle. The whine completely disappears once the temp gauge hits 210 on the dot. 209.9 and below, it gets real annoying. Going through the gate on base, I get weird looks from the guards like the Jeep is public enemy number one.

I'm not too familiar with the 4.0's as I'm coming from the Powerstroke community. Can anyone help me zero in on this issue? Thanks in advance!

 

Likely around the throttle body. Spray carb cleaner around it at idle.

It's never a bad idea to snug up your intake manifold bolts.

 

Thanks for the tip! I’ll check that out when I get home.

 

Sounds like the idle air controller isn't doing its job.

 

The IAC is nothing but an electrically controlled vacuum leak. But it can't compensate for other vacuum leaks that shouldn't be there.....