Intermittent '01 idle problem

Every 10-20 starts or so the Jeep fires up very roughly. It never happens when the engine is cold, only when warm, and typically after a 5-15 minute stop when running an errand. It starts up, but weakly, and runs really rough for a minute or two. No significant response to gentle tapping the accelerator pedal. It will sometimes respond if I really go at it, but I do not feel like revving it is wise when it's going on. Sometimes it will only do this once when the mood strikes, but a few days it's done it repeatedly.

Two instances of check engine light from this behavior: #3 misfire code the day I bought the car, and then a generic misfire code about two weeks later. The other times have not trigger the check engine light, including a couple days ago.

I've had the vehicle for a month, and this is what's been done thus far:

IAC valve has been removed and cleaned.
Connection to IAC has been cleaned with electric connection cleaner.
New NGK plugs.
Throttle body cleaned in place.

When I returned to the dealer the day I bought it, they performed the procedure that sucks a can of top end cleaner through the system, let it, sit, and then watch the smoke pour at the exhaust. They cleared the codes at that time

I have run Seafoam with each tank since.

The "trial and error" budget is empty after Christmas, so I'm hopeful someone's had the same problem and found the solution already.

Thanks!

What you are describing sounds like classic "heat soak" to me. For whatever reasons, the 00-01 are particularly susceptible to this problem.

I'd suggest you search this and other Jeep forums for "heat soak" and you'll get plenty of hits. Fixes include a timer that keeps the efan running for a programmed amount of time after you turn the engine off and some others have cut louvers into the hood to help lower engine compartment temperatures.

Here is a technical service bulletin that you may be interested in, but know that this bulletin has produced lukewarm results for those that have performed it. Good luck!
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TSB 1803103 - 4.0L ROUGH ENGINE IDLE AFTER RESTART FOLLOWING A HOT SOAK
Date: 09/05/03 (supercedes 1802702 dated 09/06/02)
Model Year(s): 1999-2004

Description: NOTE: This bulletin applies to vehicles equipped with a 4.0L engine. This bulletin involves the installation of a fuel injector insulator sleeve.

Details: Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector #3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder #3 until the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3 temperature to a point below which the fuel will not normally vaporize.

If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.

Parts required:
56028371AA Ignition Wire Shield

Repair procedure:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length. See diagram.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o'clock position.

Heat soak, a failed check valve on the fuel pump assembly, or leaky fuel injectors. And, possibly a combination of two or more of these issues.

On the 01 its most likely heat soak... fighting the same thing on mine now.

Start with the TSB and see if that helps.

This is exactly the symptoms my 2000 has been having, except it now has a popping through the intake 100% of the time, even when cranked cold.

I also noticed that the coolant was a bit low, however there is no oil / coolant mixing.

I have done the computer reset procedure with no check.

Tomorrow I plan on removing the coil pack to test it with the multimeter and check the plugs.

Thank you in advance for your help.

Rick