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Jeep won't idle when at full stop

Jparish100

New Member
Joined
Jun 19, 2021
Messages
8
Location
Idaho
Hey everyone! I'm hoping I can get some advice from you all. Today after doing some work on my Jeep TJ I took it for a drive. I stopped for a moment and turned it off and when I turned it back on the Jeep could no longer hold idle and would stall. This was not an issue before the work I did or immediately after. For context on what work I had just done, I had an issue with my HVAC not switching vents and found it was an issue with the vacuum line. I repaired the line and this fixed that issue. I then pulled out the old wiring from a disabled security system the last owner installed. I know that this security once had the ability to disable the jeeps ignition, so after unplugging any wires I would test start the jeep to make sure it would run. I successfully took all the wiring out and the Jeep still started without issue. Then after test driving this idle problem began.

Idle problem description: initially the jeep wouldn't even attempt to hold idle, but now it will attempt to but seems to stay around 500 RPM if it can even manage that.

Troubleshooting I've done: I checked the vacuum lines again and all looks good. I also reconnected everything I disconnected from the security system and this did not fix the issue.

I know there are a lot of variables here, but I greatly appreciate any input you all might have!
 

Jerry Bransford

TJ Guru Moderator
Staff Member
Supporting Member
Joined
Nov 9, 2015
Messages
24,805
Location
Fleming Island Florida
Could be a clogged/dirty IAC (idle air control) which is the source of all of the engine's air at idle RPMs. Buy a can of throttle body cleaner and spray it into the throttle body while the engine is running at idle RPMs. The IAC will suck the cleaner in through itself. The engine will die when the cleaner floods the IAC which is normal, just restart the engine and do it again and again until 1/3 or so of the TB cleaner has passed through the IAC. Don't raise the engine RPMs while spraying the cleaner to prevent the engine from dying, that would cause the cleaner to bypass the IAC. No guarantees but this could help.

TB & TPS Sensor Locations.jpg
 
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Capt'n

TJ Enthusiast
Joined
Mar 17, 2019
Messages
130
Location
Southern Oregon Coast
I know this may sound like I’m oversimplifying this but a similar idle issue has happened to me. I had my battery disconnected to do work on the Jeep. Everything ran fine prior to my work which had nothing to do with any specific electrical things. When I reconnected the battery and started it up it wouldn’t idle. It ran fine but died when I took my foot off the gas pedal. After searching the forums I read about HOW you start your Jeep after the battery has been disconnected effects the idle setting. I remembered I “pumped the pedal” a couple times prior to starting and so I went ahead and disconnected the battery again … reconnected it, and this time just turned the key without using the gas pedal. It started up fine like before but it idled perfectly and has ever since. This may not be a fix for you but you have nothing to lose trying except 5 mins of time.
 
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J

Jparish100

New Member
Joined
Jun 19, 2021
Messages
8
Location
Idaho
Thanks Jerry and Capt'n! Oddly enough, the problem resolved itself somehow. I'm going to pick up some throttle body cleaner just in case it acts up again and follow what you suggested Jerry. Thanks for the help!
 
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J

Jparish100

New Member
Joined
Jun 19, 2021
Messages
8
Location
Idaho
Well dang, I was a bit quick to celebrate.

I found out that this problem only occurs when the engine is at operating temperature. I suspected the idle air control valve is the culprit and pulled it out and found it was looking pretty rough. Gave it a good cleaning and now the Jeep will just barely hold idle when warm, but that is an improvement! I’m gonna get myself a new one and see if that does the trick. I’ll keep you all posted if it does 😁