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Low idle and stalling - '91 XJ

Old 06-25-2010, 03:39 AM
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Default Low idle and stalling - '91 XJ

My '91 XJ w/ 4.0 HO for some reason has started having a really low idle and stalls because of this. Any ideas what would cause this? All help greatly appreciated guys. Thanks in advance.
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Old 06-25-2010, 07:38 AM
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Default I also have a 1991 Cherokee - orginial owner

My 1991 Jeep Cherokee Limited which I have had since it was brand new and yes its my primary vehicle. You don't say how long you had the Cherokee , or how many miles is on it etc., has it had a major tune-up in the last 50K, if it has, its more then likely one of 2 things. The CPS ( CrankShaft Position Sensor ) or the TPS ( Throttle Position Sensor ). I know because I keep my Cherokee tuned up about every 50 to 60k, from day one, and I now just had to replace ( within 2k miles ) both of these sensors. Have these been replaced or tested ?

Orginial 91 Cherokee Owner
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Old 06-25-2010, 08:44 AM
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It could be one of 4 or 5 different sensors. You have to test them one by one or you'll end up like I did and replace every one only to have it be a DOA temp sensor.

I'd start by cleaning the idle air controller.

-E
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Old 06-25-2010, 09:34 AM
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Well I've had it for a few months and I did a motor swap and the motor I put in has a little over 100K on it. CPS is brand new. I did buy a new TPS though but I can't seem to get the T20 torx screws out. I think they may be stripped. And ideas on how to get them out?
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Old 06-25-2010, 09:42 AM
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Does this happen in gear or in park....

If this is happening when you are coming to a stop in gear you may also be looking at a torque converter.
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Old 06-25-2010, 10:42 AM
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Originally Posted by 91_XJ_Dude View Post
I did buy a new TPS though but I can't seem to get the T20 torx screws out. I think they may be stripped. And ideas on how to get them out?
Yeah that happened to me too. Had to get a lock wrench on it and move it bit by painless bit until it gets loose enough. (btw, obvious reminder to replace said stripped torque screws). Either that or my bro-in-law hammered (gently) the bit into a stripped out screw on his truck and got it firmly wedged, then applying alot of forward pressure, was able to turn the bolt with the torx driver.
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Old 06-25-2010, 10:49 AM
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Sounds like it is the idle air control motor. If it runs fine with your foot on the gas, but stalls once you take your foot off of the pedal, you IAC motor is failing to keep the idle speed up to spec. Napa has them for about 50 bones.
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Old 06-25-2010, 10:50 AM
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Originally Posted by Bustedback View Post
Sounds like it is the idle air control motor. If it runs fine with your foot on the gas, but stalls once you take your foot off of the pedal, you IAC motor is failing to keep the idle speed up to spec. Napa has them for about 50 bones.
sounds right to me too
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Old 06-25-2010, 02:24 PM
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Originally Posted by 91_XJ_Dude View Post
Well I've had it for a few months and I did a motor swap and the motor I put in has a little over 100K on it. CPS is brand new. I did buy a new TPS though but I can't seem to get the T20 torx screws out. I think they may be stripped. And ideas on how to get them out?
Take the throttle body off (takes 5 minutes, max) and then you can give the TPS screws a closer look.
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Old 06-25-2010, 02:56 PM
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I think the TPS on the HO engine is not adjustable, only the RENIX engine has an adjustable TPS. I think thats right. Just read the post again, you're wanting to replace, not adjust. I use a T20 and a 1/4 drive ratchet with a small extension.
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Old 06-29-2010, 02:19 PM
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Ok well Last night my CEL came on so i did the code trick and found that a 24 came up and that leads to the TPS.
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Old 07-06-2010, 01:44 PM
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Also this seems to happen when the motor gets to the normal running temp and it happens both in park and especially when I'm in gear with my foot on the brake.
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Old 07-07-2010, 07:29 PM
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Idle Air Control motor, replace it.
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