Jeep won't idle when at full stop

J

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!
 
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
 
  • Like
Reactions: VadeerHunter and CharlesHS
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.
 
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!
 
  • Like
Reactions: Capt'n and Jerry Bransford
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 😁
 
Removing it to clean it doesn't also get its air passages clean inside the throttle body. That's why I suggested cleaning it the way I did above.
 
Jerry Bransford said:
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.

View attachment 360493
Click to expand...

Jerry, Thanks for all your wisdom and experiences. I have 2 questions. Will any TB Cleaner work on a 2001 TJ 4.0 and do you spray the TB cleaner directly into the IAC Passage Inlet?
 
  • Like
Reactions: Jerry Bransford
Yes any aerosol throttle body cleaner will be fine. If the engine is idling as it should be it will suck the cleaner into IAC's inlet without specifically aiming the cleaner at it so long as you spray it into the throttle body.
 
I was looking at the CRC TB Cleaner at the auto parts store. Reading the directions it specifically stated it to be used on an engine that is off And all electrical connections removed??? Am I missing something?
 
MoonShadowTJ said:
I was looking at the CRC TB Cleaner at the auto parts store. Reading the directions it specifically stated it to be used on an engine that is off And all electrical connections removed??? Am I missing something?
Click to expand...
Nope that's their lawyers talking. It'll work fine when used as recommended above.
 
There is little set screw that should be under the tab where the throttle lever is. Sometimes they fall out or people take them out that is supposed to be a stopgap in case the TBI has an issue with the idle control or... It's there to maintain a fixed minimum idle speed just in case.
 
VadeerHunter said:
There is little set screw that should be under the tab where the throttle lever is. Sometimes they fall out or people take them out that is supposed to be a stopgap in case the TBI has an issue with the idle control or... It's there to maintain a fixed minimum idle speed just in case.
Click to expand...

Any pictures?
 
Top Bottom
Back