Rough idle when partially warmed up.

[punchingbag]

Howdy, folks.

First-time Jeep owner here. Joined the family Monday with a used 2024 JTMT with ~5400 miles.

Noticed a rough idle when cold Tuesday morning. (sat overnight). Took it to the dealer Wednesday, and they weren't even interested in hardly looking at it. I bought their "injector cleaner" service just to create a record of my concern and to create an initial relationship with the dealer. Their recommendation is that it has likely sat for some time. Run the injector cleaner, put a few tanks of premium in it, and drive it for a couple of months. "it should clear up".

One thread I have since read on these forums seems to describe my issue exactly. The consensus from that thread was to try to pull diag logs on it while it is doing it because if it was a "fuel" issue, it would do it the entire time it was running.

My symptoms
1. On cold start no rough idle
2. About 60-90 seconds in, the rough idle starts. It is worse with a/c on but doesn't go away completely with a/c off.
3. Feels like a single surge or miss every couple of seconds. With a/c on it is 2 or 3 surges at a time
4. The tach needle doesn't move at all during the rough idle. Even the lightest touch on the gas stops the behavior instantly. When letting off, it comes back.
5. The issue also goes away when fully warmed up.

The pictures below show the temp when the roughness starts and when it goes away.

Any thoughts from the experienced Jeep guys would be much appreciated.

Thank you, Kindly
-Travis

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[punchingbag]

Forgot to mention. For my benefit, I am sending an oil sample to Blackstone for analysis to get a baseline for the engine.

 

[bmpcamry09]

There is nothing wrong with your Jeep at all. And a fuel system cleaning service with 5000 mile was a waste of money.

These have a very aggressive variable cam and spark timing mapping when the engine is warming up, this is done on purpose to heat up the catalytic converter and engine as fast as possible and will often manifest as "rough" running. The engine will advance the intake cam and retard the exhaust cam from their base position to create a mild EGR effect and recycle hotter air through the combustion process during warm up. This is why these engines warm up so quickly. What your describing is common and nothing to worry about, a significant rough running or misfire even will cause a check engine light.

 

[punchingbag]

Thank you for the great information. This helps me a lot as I start to learn what sounds/feels normal on this first Jeep.

The first thing I noticed was how fast it warmed up. I was like, "Damn, OK then" lol.

 

[bmpcamry09]

Thank you for the great information. This helps me a lot as I start to learn what sounds/feels normal on this first Jeep.

The first thing I noticed was how fast it warmed up. I was like, "Damn, OK then" lol.

Yep! The 2.0 in the Wrangler is even more noticeable. It sounds like a misfiring farm tractor until it’s warmed up for the same reason.

 

[jelkenoverland]

Thank you for this post. I have wondered same thing about my gladiator it runs great jut has the same exact symptom. Finally an explanation that makes total sense.

 

[bmpcamry09]

Thank you for this post. I have wondered same thing about my gladiator it runs great jut has the same exact symptom. Finally an explanation that makes total sense.

No problem! I tune these almost daily and I can pinpoint and explain in painful detail nearly every unique trait of this engine. I’ve got probably 1000+ hours into these calibrations both in stock form and in supercharged form and still learn some new stuff every now and then. Feel free to reach out of you have any questions!

 

[WilldWilly]

I agree this is normal. I will say that with your truck's age, and mileage, if it sits a lot, I would keep the tank full, and treat the gas with Stabil 360.

 

[ChrisNLA]

Can confirm. Mine feels like that sometimes, but engine runs great.

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