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  #16  
Old July 26th, 2020, 09:24
CJR CJR is offline
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Re: Need help with mis at idle

Does the rough idle clear-up at higher speed? Yes, spray manifold looking for cracks, but also do a very intensive visual inspection of the manifold.

I bought my 88XJ years ago and was plagued with a rough idle. Then one day my son and did a thorough visual inspection, on a hot engine, and my son's sharp eyes picked up the hairline crack. The PO had mixed up some aluminium epoxy to cleverly cover-up and hide the manifold crack. However, when the engine heat expanded the manifold, the epoxy patch cracked and allowed extra air to enter the engine. On cool-down, the epoxy crack closed-up tight and was invisible to the eye. Also, if you have spark plug wires , check them out as well.

Best regards,

CJR
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  #17  
Old July 26th, 2020, 09:35
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by CJR View Post
Does the rough idle clear-up at higher speed? Yes, spray manifold looking for cracks, but also do a very intensive visual inspection of the manifold.

I bought my 88XJ years ago and was plagued with a rough idle. Then one day my son and did a thorough visual inspection, on a hot engine, and my son's sharp eyes picked up the hairline crack. The PO had mixed up some aluminium epoxy to cleverly cover-up and hide the manifold crack. However, when the engine heat expanded the manifold, the epoxy patch cracked and allowed extra air to enter the engine. On cool-down, the epoxy crack closed-up tight and was invisible to the eye. Also, if you have spark plug wires , check them out as well.

Best regards,

CJR
Yes it runs great under load, good acceleration, does not lurch or sputter, or appear to misfire at freeway speed or acceleration
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  #18  
Old July 26th, 2020, 09:38
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

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Originally Posted by RCP Phx View Post
You definitely need to spray around the intake while warm/running.
feel pretty confident that I have done this but will give it another shot. Going to try and go find another harness that I can put in so I can fix the one I have. Need to kept running while I work on it.
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  #19  
Old July 26th, 2020, 09:42
RCP Phx RCP Phx is offline
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Re: Need help with mis at idle

Good luck with that specially since they are very application specific. Did you read the entire thread? Out of 3 harness's all had wire degradation.
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  #20  
Old July 26th, 2020, 11:37
CJR CJR is offline
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Re: Need help with mis at idle

At this point, I'd hang a vacuum gauge on it and see what the needle movements tell you. There are many symptoms that can be diagnosed with how the vacuum gauge needle is acting. Likewise, try swapping in a spare TPS to see if there's an improvement. Based on what you've described, there seems to be an air leak at idle which smooths out on acceleration.

Best regards,

CJR
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  #21  
Old July 26th, 2020, 13:14
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

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Originally Posted by RCP Phx View Post
Good luck with that specially since they are very application specific. Did you read the entire thread? Out of 3 harness's all had wire degradation.
Yes I did and thank you very much for your insight! I am going to do what you did and make the repairs but I have to keep it running so my son can get around. I will keep you posted!
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  #22  
Old July 27th, 2020, 03:55
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Tim_MN Tim_MN is offline
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Re: Need help with mis at idle

An intake manifold leak is typically a high, or very high, idle. Idle variation is typically a sensor issue, usually the IAC, the TPS, or O2 sensors that are faulty, have wiring/fuse issues, or are not NTK.
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  #23  
Old July 31st, 2020, 08:28
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by CJR View Post
At this point, I'd hang a vacuum gauge on it and see what the needle movements tell you. There are many symptoms that can be diagnosed with how the vacuum gauge needle is acting. Likewise, try swapping in a spare TPS to see if there's an improvement. Based on what you've described, there seems to be an air leak at idle which smooths out on acceleration.

Best regards,

CJR
Ok so I decided to challenge myself and replace the injector, o2, coolant temp, TPS, MAP, Intake air, and IAC portions of of the engine wiring harness with a used harness that was intact without any broken insulation. My xj harness had numerous insulation breaks near injector 5/6 and several sensors and injectors had insulation wear at the connectors. I used a harness from an 02 WJ which was the only one available in my area. I had to splice on my XJ o2 connectors, and the TPS connector. It took me about 8-12 hours being extra cautious, to make sure I did not mis anything and to make sure I got it right. A few wires were different colors than my xj so I took extra care to make sure I got it write. I sent most of the wires directly back the the PCM connector but spliced the grounds and 5 volt volt sensor power mid way.

So was there improvement? I would say slightly.

After the harness was done, I replaced the TPS with a new MOPAR and there is no difference so far.

After replacing harness and TPS, I did notice a hiss from the throttle body area at idle and upon investigation found it coming from the the small opening on the inside of the TB that serves the IAC. I assume that is normal???

I Will take a video of the vacuum gauge and post.

Should I consider replacing the PCM?
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  #24  
Old July 31st, 2020, 08:33
RCP Phx RCP Phx is offline
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Re: Need help with mis at idle

It's very possible. Re-read my post #24 where I replaced the ECU.
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  #25  
Old July 31st, 2020, 18:34
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

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Originally Posted by RCP Phx View Post
It's very possible. Re-read my post #24 where I replaced the ECU.
Forgive my ignorance. Your post #24? Can you provide a link?
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  #26  
Old July 31st, 2020, 18:43
RCP Phx RCP Phx is offline
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Re: Need help with mis at idle

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Originally Posted by RCP Phx View Post
A little long, but skip to post #39 for the start of the details!
https://naxja.org/forum/showthread.php?t=1145993
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