After startup, my Jeep has a strange, surging idle. I have no tachometer, but I can hear the engine speed going up and down, maybe a couple hundred RPMs at most. Each "up" or "down" cycle lasts about a second to two seconds. After driving for a while and the engine's warmed up it will go away and just idle at it's usually low, loping pace. I've considered replacing all of my vacuum lines (they're getting old and cracked), and I've also considered cleaning/replacing all of the sensors on the intake. I've already cleaned the IAC and run plenty of injector cleaner. This idling thing has been going on since my parents bought it 100k miles ago. Is this idling thing normal for all injected 4.0s? What things should I diagnose first and what should I consider replacing?

Rob

 

Anybody have any experience with this?

 

bad vacumlines could easely be the problem. make sure that they are all perfect.

good luck

 

Can someone identify those fire sensors on the back of the intake manifold for me? I know one is the MAP, but not the others. Also, is there just one O2 sensor on my jeep?