It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
Best place to start with an idle problem is by removing and cleaning the idle air control. They get carboned up over miles and time.
The IAC is mounted on the back of the throttle body. 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 moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, 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.
CLEANING THE IAC
1. Remove the IAC with a torx driver (2 bolts, one may be kind of hard to get to)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, won't harm the coatings on throttle bodies and is formulated specifically for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you could damage it.
4. Also thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner
5. Consider cleaning the entire throttle body itself and all associated linkage as long as you’re at it
6. Reinstall IAC and check idle quality
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!