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Replaced CPS & CKS - Now Slight Stumble at Idle in Gear

Emerscape

NAXJA Forum User
Location
Boston, MA
I had my CPS and CKS replaced last week due to a no-start condition. Pulling my jeep out of the parking garage spot this morning and making a hard right turn I feathered the gas and saw the RPM needle drop low and the engine sort of stumble. Gave it a little more gas and it was find. I noticed that if I'm sitting at idel and give it a little gas that there is an ever so slight stumble before the RPMS rise. Could it be an issue with my TPS or AIC?

It's a 2000 xj with 135k miles.

Thanks,

Pete
 
I'd bet TPS or IAC, yes.

Might want to measure before replacing though - neither one is particularly cheap.
 
Clean the IAC.

Use some Techron or SeaFoam fuel injector cleaner.

Simplest and cheapest solutions first option, new parts second option.
 
I believe it's a T20 bit, and most of the screws are tamper-proof- ie, have a small raised stud in the center. Most of the bits I've purchased have the small recess to accommodate them, but make sure yours do.
 
I've never seen a tamperproof one there, though I've only had to mess with it on my 96 so far. You should probably get a tamperproof set anyways just in case you want to replace the multi function switch sometime in the future.
 
edit- Maybe it was just the IAC housing screws that were tamper-proof- I sold my spare TB, so I can't verify that at the moment.
 
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The Idle Air Control (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 JEEP 4.0 IDLE AIR CONTROL

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)

"Gently" wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

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 is best for this task. 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 or create problems with the function of this unit.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality
 
 
thanks for the detailed instructions it's greatly appreciated.

I had my xj in for service a couple weeks ago getting my brakes adjusted and having a cooler line replaced. I also had them clean the throttle body. Would they have cleaned the IAC during the process to clean the throttle body?
 
I had my xj in for service a couple weeks ago getting my brakes adjusted and having a cooler line replaced. I also had them clean the throttle body. Would they have cleaned the IAC during the process to clean the throttle body?

Hard to say. They might have or they might have just sprayed some throttle body cleaner into the TB. I'd ask the technician that performed the work.
 
Should they have? I've never seen inside the throttle body - will do when I clean the IAC but just wondering. I'll go back to them if that is the case.
 
... could it be an issue with the CPS and/or CKS that they replaced?

You won't know until you clean the IAC, will you.

Might be a CPS issues or a wiring issue or maybe just a dirty IAC. Always start any trouble shooting with the simple and easy stuff, inspect for damage, clean, adjust, test.
 
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