When I'm driving, even though I'm holding the accelerator steady, the engine idle speed will increase and then decrease. The change in idle seems to cause the transmission to downshift sometime at around 60mph, while driving on the expressway. It seems to idle high when the engine is cold and will increase and decrease idle speed a lot. What would cause this?

 

Welcome to CF!

Two things off the top of my head. Check your IAC (idle air controller) and the hose to your MAP (manifold air pressure) sensor.

Is this a 4.0 or a 4.7 V8?

 

It's a 4.7 HO.

 

Okay, I'm a little out of my league here. I've owned a couple of 4.0s, but haven't even been in the presence of a 4.7. In all honesty, I couldn't tell you where to look except to check those things.

 

Just got this Jeep and haven't had much time to look around at it much. Well, your idea about the hose to the MAP helped and it turned out to be a simple fix. The clamp was loose at the throttle body intake. Tightened it up and that fixed the problem. Not sure what normal is for this engine but seems like it's idling more normal now. Thanks for your help!

 

Glad to help. My 4.0 starts cold at 1000 and then settles down to 750.