Crazy rpm, need help!!
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Member
Joined: Jul 2008
Posts: 151
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Model: Cherokee
Crazy rpm, need help!!
Hello guys i need your help! For a while now the rpms on my 89 xj from time to time while start going crazy, i start the truck it runs great for a bit then the rmp will start jumping around and make my truck die, i start back it up runs well again then a few miles it does it again. Im reaching the end as i cannot find what is wrong with it. And it seems to be getting worse , Now when i turn on the truck and step on the brake the rpm goes down and it dies. I already replaced cps sensor, tps sensor. Any ideas at what should i look for next would be great 
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Joined: Sep 2012
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Originally Posted by jkshavoc
Hello guys i need your help! For a while now the rpms on my 89 xj from time to time while start going crazy, i start the truck it runs great for a bit then the rmp will start jumping around and make my truck die, i start back it up runs well again then a few miles it does it again. Im reaching the end as i cannot find what is wrong with it. And it seems to be getting worse , Now when i turn on the truck and step on the brake the rpm goes down and it dies. I already replaced cps sensor, tps sensor. Any ideas at what should i look for next would be great
Seasoned Member
Joined: Jan 2011
Posts: 303
Likes: 4
From: Austin
Year: 1987
Model: Wagoneer
Engine: 4.0
Based on your statement that stepping on the brake makes it worse, I would suggest you look for a vacuum leak. Stepping on the brakes uses the brake booster which runs off of vacuum. Look/listen around the booster for a leak, then start working the other vacuum lines. There should be a vacuum diagram under your hood. Good luck!
CF Veteran
Joined: Apr 2009
Posts: 1,601
Likes: 1
From: Kalamazoo, MI
Year: 2000
Model: Cherokee
Engine: 4.0L with throttle body spacer and cold air intake, bored throttle body, #784 injector upgrade
have you cleaned the Idle Air Control? Sometimes carbon builds up in them and causes them to stick creating strange rpm issues.
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Member
Joined: Jul 2012
Posts: 141
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Model: Cherokee
I'm going through the same thing you are. I've tried clearing the computer to reset the iac no luck, replaced it no luck, tried running it with out the sensor started once idled perfect then wouldn't start up after that. Looking for vacum leaks atm, did you recently rebuild the engine? i did and it started after that.
Thread Starter
Member
Joined: Jul 2008
Posts: 151
Likes: 0
Model: Cherokee
I'm going through the same thing you are. I've tried clearing the computer to reset the iac no luck, replaced it no luck, tried running it with out the sensor started once idled perfect then wouldn't start up after that. Looking for vacum leaks atm, did you recently rebuild the engine? i did and it started after that.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
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From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I'm going through the same thing you are. I've tried clearing the computer to reset the iac no luck, replaced it no luck, tried running it with out the sensor started once idled perfect then wouldn't start up after that. Looking for vacum leaks atm, did you recently rebuild the engine? i did and it started after that.