2001 XJ. I have a low idle RPM and have been trying to hunt down the problem for a couple of weeks. Its kind of got an intermittent stutter once warm sitting at idle. Checked all vacuum lines, everything checks out. Checked injectors, all fine. Checked fuel pressure (Orielly's rental tool) and its holding at 50 psi but it is rapidly bouncing. Could this be the regulator? If the regulator is bad wouldn't PSI on fuel pressure decrease after shut down? It does not in my case.

My ignition coil rail is new. Spark plugs fairly new. I'm running out of things to check. I haven't ruled out my timing but it fires right up at start. Any thing I could be overlooking?

 

Clean the throttle body and pull out the Idle Air Control (IAC) and carefully scrub it down too with throttle body cleaner. Check the throttle position sensor while you are there. Replace the fuel filter too. Check that the MAP sensor vacuum line is not clogged or damaged.

 

I have gone through the entire vacuum system. Replaced AIC, TPS, and MAP sensors, and cleaned throttle body with no difference in idle. The engine seems to be "stumbling" a little at idle. Could my timing be off (even if that's the case would idle be low)? This is an 01 so I have the coil pack, no distributor (coil pack is about a year old).

I have no codes so its seems it is a fuel/air/ignition issue. Its just really difficult for me to know which direction to go in now. Guess drop the fuel tank and see if there is anything going on in there, maybe replace the whole fuel pump, filter, regulator (I think the whole assembly is a little over a hundred bucks). The thing is my pressure is reading good, even if its a fuel issue how would that affect the idle if pressure is good? The Jeep is running great under load, but once it gets hot and is sitting at idle it gets rough.