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Unread 08-11-2012, 07:01 AM   #1
98jgc
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2005 WK 
 
Join Date: May 2006
Location: Oneonta, NY
Posts: 434
88 Cherokee 4.0 miss

Hi there

Hope you have suggestions for this one:
Lately occasionally the engine totally loses power for approx 1 second, then runs on. It doesn't happen every day, maybe one out of five days, but more and more. It's always 1-3 miles from start, so it's not when it's very cold, neither when it's hot, but during warm up. Sometimes it happens during acceleration or driving, sometimes during idling (then it stalls and need to be restarted)

I've tried to have it idling and wiggle all wires and vacuum lines etc., no result.

Any suggestions are welcome.

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Unread 08-11-2012, 07:45 AM   #2
tjwalker
It's the crank sensor!
 
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1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
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May sound like a broken record with this response, but what is the status of all tuneup hardware?

Fresh Champion plugs gapped to .035, new quality plug wires, distributor cap, rotor, and fuel filter.

Gotta be sure that is good before looking elsewhere (testing fuel pressure, testing engine management sensors and egr, etc).
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99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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Unread 08-11-2012, 07:48 AM   #3
98jgc
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Thanks for input. Plugs are new, the rest not. I would say though that it doesn't feel like that kind of miss, you know the occasional one cylinder. It's total loss of power.

But I'll start there if I don't get other suggestions. Thanks
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Unread 08-11-2012, 08:00 AM   #4
crzmn1
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i had a similar problem with my wifes 93 xj it turned out to be the throttle body needed cleaned due to black soot, so i tore it apart and cleaned it now it runs fine you might check that too
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Unread 08-11-2012, 08:43 AM   #5
98jgc
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I've cleaned that earlier, because it would stall at a red light when in 4wd and turning the steering wheel. Helped a lot. Just redid it as you suggest, we'll see...
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Unread 08-11-2012, 05:54 PM   #6
tjwalker
It's the crank sensor!
 
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Location: Central Minnesota, MN
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Never a bad idea.....
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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 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.

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
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99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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