2005 Wrangler LJ Rough Idle No Power

OriginalGOB

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Joined
Jan 10, 2023
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16
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East Tennessee
I have a 2005 Wrangler LJ with the 4.0. I have been getting a CEL for P0300, P0303, P0304 and P0431 randomly. Each time I reset the codes they randomly come back. I wasn't really worried because it was running fine. It started to have a slightly irregular idle so I replaced the spark plugs with Autolite XP985 plugs. I also tested the continuity of the coil pack. Cylinders 1&6, 2&5, 3&4 all read 15.54 on the ohm meter. I'm sure this is unrelated but wanted to include it for the history, the vehicle ran fine for two weeks then I started having an issue where the CEL would come on and my engine temp would max out until I slowed down. I replaced the entire cooling system (radiator, upper and lower hose, water pump, thermostat, fan clutch and gaskets) to correct this issue. My issue now is that my Jeep idles rough, it will not rev above 1500 RPMs, and it will only move on a flat surface less than 1 MPH. The last set of CELs that I had were: P0300, P0303, and P0304. I reset them to see if I could get a fresh set of codes without any luck. It seems to me like the cold air intake is sucking in a lot more air than it previously did. I cleaned the throttle body and checked the connections. Today I cleaned the ECM connections and noticed that the first connection had engine oil in it so I cleaned it out. I have attached the BlueDriver live data for reference. Thanks in advance for any help you can provide!
 

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Could it be as simple as a vacuum leak from something that got accidentally unplugged?

How's your wiring harness look? I think I recall a forum post where someone reported a faulty oil pressure sensor filling their ECU with oil.

-Mac
 
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Could it be as simple as a vacuum leak from something that got accidentally unplugged?

How's your wiring harness look? I think I recall a forum post where someone reported a faulty oil pressure sensor filling their ECU with oil.

-Mac

Thanks, I was thinking the same. I have sprayed brake cleaner on the vacuum lines without any difference in the RPMs. The wiring harness is pretty crusty but seems to be completely intact, I sprayed it out really good with compressed air.
 
A vacuum leak will cause high RPMs. When people don't get the intake manifold seated properly, it will rev to redline on startup.
 
Update: I disconnected both upstream o2 wiring harnesses without any change in the idle or RPM speeds. I also measured the temperature about an inch before and after the catalytic converter, on the engine side the temp was approximately 100 degrees cooler than the exhaust side.
 
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@OriginalGOB Do you get any hard shifts in the morning? Have you had the Jeep smoked for exhaust and/or intake leaks?

Welcome to the forum!

Mark

Thanks so much @Wranglerfix! Unfortunately, I can't get enough speed (if any) to get it out of first gear. I have not had it smoked for leaks, that might be on my short list of next things to try .
 
Got it. Our PCM will correct a lot of the issues that you are experiencing. I would hold off on the smoke tests until you install our pcm. You can call me to discuss in further detail if you'd like. God knows I like to talk! :)
 
@Wranglerfix thanks for taking the time to speak with me today. For my next steps, you mentioned testing mine to ensure it is bad. From there should I have you all repair it or purchase a new one?

-Greg

Good morning Greg,

Your OEM pcm is not repairable no matter what you might read online. It is not worth the lead to shoot once it fails. However, stick it on the shelf for emergency backup purposes. If anything ever goes wrong with our pcm #1 it is repairable, #2 You're Jeep still functions with your old pcm!

Thanks,

Mark
 
Bad news. I received the new PCM this morning, installed it and unfortunately it didn’t fix any of the issues. I also did a cheap vacuum leak test by putting a lit cigar up to my brake booster line and couldn’t see any vacuum leaks…I’m really scratching my head now
 
I measured the temperature about an inch before and after the catalytic converter, on the engine side the temp was approximately 100 degrees cooler than the exhaust side. Should I do something different? Thanks
 
Yes, you need to pull the O2s out or drop the mini cats down from the manifolds. If the cats are clogged, the engine can't move the exhaust out. If you give the exh somewhere to go, the engine will run it that is the problem.