Hi everyone, I found an older unresolved post that is exactly the issue I am having:

"I have a 1998 Cherokee Sport, 4L 6 Cylinder engine. 146,000 miles.

For about a year and a half I have an issue with jerky acceleration at lower speeds. Around the same time I started experiencing some problems with a rough idle. When the engine is cold it idles very loudly and the RPMs oscillate in an inconsistent pattern. During this, the exhaust system is very loud and is shaking underneath the vehicle. On several rare occasions the engine has shut off because the RPMs have dropped so low.

I'm not sure if the two problems (idle and acceleration) are related. It feels like the same thing because my RPMs also fluctuate when driving at lower speeds. When this happens and the RPMs drop, it feels similar to running out of gas. Also when the jerky acceleration happens, I hear a clunk/click and I can feel that clunk/click in the gas pedal. Spark plugs were replaced just a few months before this all started.

This happens very inconsistently. I had a mechanic look at it, but it wouldn't happen when he was in the car. Lately, it has become less inconsistent and happens almost every time I drive. Outside temperature seems to have no effect. It almost always stops after a few minutes and the engine is warm. But even this is inconsistent as sometimes I will drive for a long time, stop the car to gas up, and the problem is back even though the engine is plenty warm. The only consistency is that it's always at the beginning of my drive. This never happens after accelerating away from a Red light for example."


Any thoughts/ideas/similar experiences?

 

Every 30,000 miles the 4.0 should get plugs, wires, cap and rotor.

The throttle body should also be cleaned at that time. CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY AND IAC CLEANING

OCTOBER 30, 2015 SALAD 24 COMMENTS
Originally by TJWalker of CherokeeForum & JeepForum



The Idle Air Control (IAC) is mounted on the back of the throttle body (front for ’87-’90).

The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed.

Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

1. Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On ’91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
2. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
3. Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
4. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner.
5. It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled.

Revised 1-31-2016

 

George, in addition to doing the basics as above, check for vacuum leaks, AFTER you've done those basics.