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Unread 09-15-2012, 10:29 PM   #1
TheComancheKid
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Join Date: Sep 2012
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got me a 88 mj

Its a 88 jeep Comanche for 150000k miles its got 4.0 5speed i paid 1150$ for her overall it runs and drives good but it runs good while ur moveing and keeping the Rs up but wants to stall when i stop at lights and at idle the rps jump and the truck wants to stall i put a new fuel filter spark plugs cap and rotor and wires does anyone have opinions on how i can fix this or had the same problem id appreciate at

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Unread 09-16-2012, 01:50 AM   #2
dkroll
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1989 MJ Comanche 
 
Join Date: May 2008
Location: Independence, Missouri
Posts: 185
I had the same problem. I took it up to the dealership, and the guy I talked to, bypassed some vacuum hoses and it has been running fine since. I know the part he bypassed, but don't know why he did it nor know that vacuum path. I will do some research in this area and get back at you. It made a nice big difference, just don't know enough to explain yet. Something to do with the emissions though.
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Unread 09-16-2012, 08:44 AM   #3
97_4popper
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1990 MJ Comanche 
 
Join Date: Jan 2005
Location: Guston, KY
Posts: 463
Check your IAC (Idle Air Control).
It's attached to the throttle body.

Comancheclub.com Go over there for all you need to know about these trucks.
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90 MJ 4.0 4X4 5sp LB Pioneer Big Ton.
Truck contains parts from 3 MJs, 2 XJs, 1 TJ and a dishwasher.
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Check out comancheclub.com...
My build thread: http://comancheclub.com/forums/viewt...hp?f=7&t=27756
Wifes: 97 TJ 2.5 4X4 5sp 31's stock. . . Slow but; reliable.
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Unread 09-16-2012, 09:34 AM   #4
cruiser54
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1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 10,319
Start here:

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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
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Unread 09-16-2012, 09:35 AM   #5
DeejayZeejay
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1994 ZJ 
 
Join Date: Mar 2012
Location: Macomb, Michigan
Posts: 325
My 88 does the same thing... I'm going to replace my Cps soon. When it gets hot, it wants to stall. Nice find though. Hows your floorboards?
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Unread 09-16-2012, 09:39 AM   #6
cruiser54
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1990 MJ Comanche 
 
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Quote:
Originally Posted by DeejayZeejay View Post
My 88 does the same thing... I'm going to replace my Cps soon. When it gets hot, it wants to stall. Nice find though. Hows your floorboards?
YOU should clean your throttle body also if you never have.

CPS is not a likely suspect for hot stalling. Hot and not starting, yes.

Any of you guys done the recommended ground refreshing? C101 connector refreshing? If not, you oughta. If you don't you can spend lots of time and money replacing sensors unnecessarily.
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Unread 09-16-2012, 11:59 AM   #7
DeejayZeejay
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1994 ZJ 
 
Join Date: Mar 2012
Location: Macomb, Michigan
Posts: 325
Mine will stall when hot. Stuck in traffic and wont start after. I started going through the grounds but not all of them.
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Unread 09-16-2012, 07:57 PM   #8
TheComancheKid
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Join Date: Sep 2012
Posts: 3
Ill check the iac sensor i haf an ifea it mite be that and the floorboards are mint no rot or rust anywhere i love it alredy
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