Hi, I own a 1996 Jeep Cherokee SE with the 4.0 liter I6. Completely stock, 183,000 miles. I recently noticed that the engine (even when completely warmed up) idled at 1,000 RPM, when it normally idles at around 750. If I leave it for an hour or so, and come back, it will start, idle down to around 750, then go up to about 1,000 RPM, and stay there. As far as I can hear, there are no vacuum leaks. I also cleaned the idle air control module (still did the same thing) and I recently cleaned the throttle body (which this issue then started a few days after). Thanks for any help!!

 

You can't hear small vacuum leaks, so it's time to start looking for vacuum leaks. You are use ether (starting fluid) or something like propane. Run the engine, then systematically squirt the ether every place there is a possible vacuum leak (which is a lot of places). Not a steady stream - just short bursts. The idea is that the ether will be sucked in by the vacuum and cause the engine to speed up.

Start near the throttle body so that as the engine warms you are working away from the exhaust manifold. Ether and a hot exhaust might be a bad mix. Do this outdoors, not in your garage! Don't just spray and spray and spray. You want to know when you get to the place where the leak is, so you must be methodical and patient.


On another note, sometimes the IAC is too far gone for cleaning to help.

 

And, make sure all your intake manifold fasteners are snug. they tend to loosen up.