'99 Jeep Cherokee not idling
 

My son has a '99 Jeep Cherokee with the inline 6 that is acting a little funky. From time to time it will die at idle. As long as I have the revs above idle it's fine. And once it warms up it does fine. Do you guys think this is a fuel pump or fuel filter issue? I do not have a gauge to determine fuel pressure.
Thanks in advance for the suggestions.

Check engine light on? If so, read the code or codes to get a starting point.

Short of that I would try cleaning the MAF sensor, if equipped as well as checking for loose broken vacuum lines.

Air filter clean?


EDIT--I did a search on the web and found that it COULD be the Idle Air Circuit sensor.

Throttle position sensor dirty?

First place I would look is on the side of the intake manifold, there two vacum lines that are connected there, and I see them leak all the time. I think there are 90 elbows on them that lead to plastic tubing, but you can easily cut them off, and make a repair with straight vacum tubing .
If no vacum leaks are found, I would check, and clean the throttle body, then re set all adaptives . Not sure, if you can do this without a scanner, but , after you clean the throttle body, maybe try disconnecting the battery for 10 minutes or so, and then let it re-learn how to idle.
Keep us posted, this should be an easy one.

I had a 99 Grand Cherokee Laredo with 4.0l that had a similar problem. Would not start without keeping foot on gas and would not idle. Throttle position sensor was bad.

Usually a dying fuel pump can be temporally corrected by banging on the fuel tank with a rubber mallet (near the fuel pump location.) Dying fuel pump is usually precipitated by a more persistent louder whine from the pump. Clogged Fuel filter will usually not clear itself up.

Thank you guys.
I'll try it out this weekend and let you know how it goes.

Also clean the throttle body. Gunk builds up around the butterfly and the IAC motor cant keep up at cold idle.

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Every XJ that i have owned would stumble the idle once idling for longer then 5 or so mins. Very common.
I would replace the fuel filter as they are only 10 bucks at napa.

Clean throttle body. Make sure you get no fluid into IAC and TPS. Most likely need a TPS as well but you can try cleaning IAC area well. CPS can cause stalling but not only at idle - it would happen all over the powerband but mostly when hot and no airflow (idling). CPS failure would be my second guess with first being TPS.

Cleaned the throttle body and IAC. So far so good.
It was pretty dirty.
Thanks again for all the input. I really appreciate it.

Open loop is where the problem is.
Old school.