"Runaway" revs upon startup. WTH?! Anyone else?

[Raydar]

I started the Jeep a little while ago. (It had been sitting for a couple of hours, but was not "stone cold".) As soon as it started, it revved up like I had my foot on the gas, pressed to the floor. (I didn't. Had my feet on the clutch and brake. ) I quickly pressed the button again, to stop the engine.
I checked the floor mats and all the other stuff to make sure nothing had the pedal jammed up. Nothing was amiss. Has anyone else experienced this?
Second question... I'm assuming that the PCM has a rev limiter programmed into it, to prevent damage in case of an over-rev situation. Is that assumption correct?
The Jeep is a 2021 JLU Sahara. 15K on the odo. We've had it less than a month.
Thanks!

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[Tethmes]

A cold or cold-ish M/T equipped JL will rev high in certain circumstances, usually in the 2.5-3.5k range, and usually when first getting started. The most common scenario is as follows:

Engine was still running at 1k+ rpm during it's warm up cycle when you got underway. You pulled down your driveway/across a parking lot and clutched in when coming to the end/exit. This is when the RPM's shot up and being the first time it happened to you, freaked you the hell out! That was my first experience with it anyway, and is a recurring theme when these threads pop up. :P

Anyway, if that, or something similar is what happened then it's perfectly normal. Annoying, but normal. If it red lined or something, then that is not normal and I'd probably get it looked at.

Cheers!

 

[Raydar]

Thanks for the comment.
No. I'm used to the high idle during warmup. That doesn't bother me a bit. (Well... it's kind of annoying, but it is what it is.)
But this was a redline - or nearly - situation. I didn't sit there and watch exactly how high it revved. I hit the button to kill it, before a piston came through the hood. Wifey even heard it in the house and asked me what it was doing, when I came back in, a while later.

If it happens again, I'll get it looked at, but if they can't duplicate it, we know how that will work out. Kind of why I'm asking here. Wondering if anyone else has seen this.
I've got a scanner, and can troubleshoot. But if the condition isn't a "hard fail", then all I can do is look at the usual suspects. Throttle pedal, and throttle actuator. Maybe a connection.

 

[m3reno]

It happens to me although not to redline. It will happen usually when warm, I'll come to a stop and my Jeep would rev to 2000 ARPM then drop back down. A bit annoying.

 

[Old Jeeper]

I started the Jeep a little while ago. (It had been sitting for a couple of hours, but was not "stone cold".) As soon as it started, it revved up like I had my foot on the gas, pressed to the floor. (I didn't. Had my feet on the clutch and brake. ) I quickly pressed the button again, to stop the engine.
I checked the floor mats and all the other stuff to make sure nothing had the pedal jammed up. Nothing was amiss. Has anyone else experienced this?
Second question... I'm assuming that the PCM has a rev limiter programmed into it, to prevent damage in case of an over-rev situation. Is that assumption correct?
The Jeep is a 2021 JLU Sahara. 15K on the odo. We've had it less than a month.
Thanks!

YES: Mine does it from time to time. It will 'take off' and get faster and faster to about 1500 rpm +/- and then drop back after a bit. Its very irregular and will sometimes go weeks and not doing it.

I believe the ECM does have a rpm limiter, I know my Ford F 450 has limits too, only it operates as a speed limiter, my max is 87 mph.

 

[autotragic]

No worries you definitely have a rev limiter. I don't think I've heard of a factory engine especially fuel injected engine not having a rev limiter since the 90s at least. Sometimes there's even a separate rev limiter for park and neutral or in gear.

 

[Chris A]

Had this happen years ago in Ford Excursion. Was the throttle position sensor. Guessing they still have these devices on engines.

 

[AcesandEights]

It's normal.

 

[Boxcar Willys]

A cold or cold-ish M/T equipped JL will rev high in certain circumstances, usually in the 2.5-3.5k range, and usually when first getting started. The most common scenario is as follows:

Engine was still running at 1k+ rpm during it's warm up cycle when you got underway. You pulled down your driveway/across a parking lot and clutched in when coming to the end/exit. This is when the RPM's shot up and being the first time it happened to you, freaked you the hell out! That was my first experience with it anyway, and is a recurring theme when these threads pop up. :P

Anyway, if that, or something similar is what happened then it's perfectly normal. Annoying, but normal. If it red lined or something, then that is not normal and I'd probably get it looked at.

Cheers!

I've got the same problem. It has happened to me 5 times. The first 3 times were okay as it just shot up to 3,000 RPM or so. But the last 2 times, right up to redline before I hit the kill button. I've got the 2014 Willys with the Pentastar 3.6 and a manual transmission. This happens when at idle and happened as the revs went down between shifts. Of course, no codes are registered on the on-board and the dealer can't replicate it, and are too cheap to replace any component like a sensor or the ECM, that could actually send the engine revving. So I'm trying my BLUEDRIVER OBD2 scanner in real-time scan mode and driving it till it happens again, and then I might have something that the moron's can use. I'll keep you posted.

 

[Raydar]

Had forgotten about this thread. Between then, and now, it's happened maybe two more times. The last time was only a couple of weeks ago.
I will state, now, that there is the largest possibility that I had my foot on the gas, as well as the brake. (And of course, the clutch.)
But whether it was random, or just "me", it hasn't been problematic enough to worry about, in any event.
Thanks, guys!

 

[YJdude]

I've never messed with computer modifications in the JL, but does pedal commander or something similar eliminate the cold high idle BS? I absolutely despise it. I can also attest to the random revs even while rolling 5-8 mph in neutral. Its dumb AF.

 

[alphawolff]

I've never messed with computer modifications in the JL, but does pedal commander or something similar eliminate the cold high idle BS? I absolutely despise it. I can also attest to the random revs even while rolling 5-8 mph in neutral. Its dumb AF.

No, it's just how the engine controller is tuned. It's trying to warm the cats up ASAP for cold starts. It's especially annoying in the manuals. Usually only lasts for a minute or two.

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