'21 Manual "accelerates" hard on its own in 1st & 2nd w/0 throttle

[JLNOLA]

I've got 2021 Sport S manual transmission with just over 1,000 miles and from time to time when I'm in 1st gear or have just shifted into 2nd it "accelerates" without much or any throttle. I've only had it happen when I drive after being parking overnight and it doesn't happen every time.

Here's an example; there's a bunch of road work happening around my house so lots of very rough road and obstacles so I'm going pretty slow, I'll pull out of my drive way and hit revs to shift into 2nd so I make the shift and when the clutch gets fully released the Jeep basically takes off like I'm on the throttle but I'm either giving it very little gas or none at all. By the time I've made a couple of shifts between 1st and 2nd getting out of my neighborhood it stops doing it. I've almost wrecked a couple of times when I've shifted into 2nd right before making a turn and then it just takes off on me and there are cars parked on a narrow street and it jumps forward on me pretty hard.

Any thoughts on this? Thanks

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[BritishGuy]

I've experienced something similar - I think the reason is because you've got higher RPMs on a cold start as the engine is still super cold, so instead of idling at say 800rpms, you're idling at 1100. After starting my 2019 JLUR and throwing it in first gear, I can launch it out of my driveway and onto the street by barely hitting the gas, sometimes without even touching it.

I'm pretty sure it's normal until the engine warms up a bit and the RPMs drop down to the usual idle speed....but be ready for it while things are still cold.

 

[neil]

IDK if on sport, but there is a setting for maintaining revs when shifting and also a rollback prevention setting.

Try those.

 

[Elsinore73]

Mine does this only when cold. I assumed it was just the high idle on a cold start. I know what you mean though, it takes off in 2nd with zero throttle input.

 

[JLNOLA]

I've experienced something similar - I think the reason is because you've got higher RPMs on a cold start as the engine is still super cold, so instead of idling at say 800rpms, you're idling at 1100. After starting my 2019 JLUR and throwing it in first gear, I can launch it out of my driveway and onto the street by barely hitting the gas, sometimes without even touching it.

I'm pretty sure it's normal until the engine warms up a bit and the RPMs drop down to the usual idle speed....but be ready for it while things are still cold.

"launch" is a good description. I assumed it was a warm up situation but I've never experienced it with other manuals I've had.

 

[nomographer]

What rpm do you get feathering the throttle in neutral these conditions? Is the rpm actually elevated when you're shifting into 2nd? How much speed is it actually adding?

 

[JLNOLA]

What rpm do you get feathering the throttle in neutral these conditions? Is the rpm actually elevated when you're shifting into 2nd? How much speed is it actually adding?

Sorry, I'm not entirely following your questions/wording. Hard to say how much speed it would build on its own if I just let it go since I depress the clutch pretty quickly to make the launch/jump/lurch stop because it gives the feeling of not being in control of the vehicle and it tends to happen on narrow neighborhood streets with lots of parked and moving cars.

 

[ChromeToaster]

While I will say mine does hold revs when I wish it wouldn't, its not something that will just launch unless you are dumping the clutch. Now what makes me mad is off road in 4low the engine will seem like it wants to revmatch for me after I put it in neutral with the wheels turning, its like it thinks I'm going to downshift or put it back into gear when I just intend to coast for a little.

 

[Rico1111]

I thought I would chime in and say (not that this is your scenario)...I have driven manuals my whole life and when I got in mine for a test drive, it was as if I had never driven one at all! I drove it home from New Hampshire and all was fine! I had to get used to the lightness of both pedals and the grab points. I had back surgery a few years ago and the nerves in my feet are damaged so that I have numbness in my feet and It really was a learning curve with this manual. Having said that, 1st gear for me was the problem ....being so short and not knowing where it grabbed.....once I got used to the grab point I was fine . I had a Mini S that used to give your left leg a work out when rowing the gears so compared to that I actually was thinking there might be something wrong with the clutch, of course there was not. Just different mechanics, I actually love this manual now!

 

[JLNOLA]

I thought I would chime in and say (not that this is your scenario)...I have driven manuals my whole life and when I got in mine for a test drive, it was as if I had never driven one at all! I drove it home from New Hampshire and all was fine! I had to get used to the lightness of both pedals and the grab points. I had back surgery a few years ago and the nerves in my feet are damaged so that I have numbness in my feet and It really was a learning curve with this manual. Having said that, 1st gear for me was the problem ....being so short and not knowing where it grabbed.....once I got used to the grab point I was fine . I had a Mini S that used to give your left leg a work out when rowing the gears so compared to that I actually was thinking there might be something wrong with the clutch, of course there was not. Just different mechanics, I actually love this manual now!

I'm very happy with it overall. Just a weird thing that happens occasionally and it seems to be related to slightly "cold" temperatures first thing in the morning. I'll make a very smooth shift into 2nd at around 12-15 mph and as soon as I'm off the clutch it just kind of takes off. Typically it happens as I'm nearing a corner or stop sign and I'm shifting into second to essentially coast through the turn or roll up to the stop sign but it starts pulling like I'm on the throttle a little. When it happens I'll depress the clutch, shift to neutral, back into second and then let the clutch out. Normally on the second time I put it into 2nd it doesn't do the pull. Sometimes I'll just coast to a stop sign and when I take off again it's normal.

 

[Overland Productions]

turn off your "send it" button. I bump mine all the time.

 

[HeavyUser]

I'm very happy with it overall. Just a weird thing that happens occasionally and it seems to be related to slightly "cold" temperatures first thing in the morning.

What you are describing here sounds completely normal to me. On a cold start, cold day, when I first turn over the jeep and put it into gear my idle rpms are much higher than when the engine reaches temp. This in turn effects the idle rpms when I'm in first or second gear, they are higher resulting in the Jeep is pulling itself along quicker then when the engine reaches temp.

 

[JayJay]

I've almost wrecked a couple of times when I've shifted into 2nd right before making a turn and then it just takes off on me and there are cars parked on a narrow street and it jumps forward on me pretty hard.

Something happened to me this morning that made me remember this post. 2020 JL, 3.6 and automatic - was on a two track forest service road that was rocky and muddy so going slow. Had just exited a sharp, uphill turn in 4 high. I had the transmission in 1st gear in manual mode and was light on the gas at around 1000 rpms. Suddenly the engine revved as if I was full on the throttle. I hit the brakes and the engine dropped back down to an idle. There's no doubt that if we had been on pavement in stop and go traffic I would have nailed the car in front of me. It's the first and only time that it has done this in 8,500 miles but it sure got my attention. I'll probably drop it by the dealer in the next few days and see what they have to say.

Later,
Johnny

 

[intentsrig]

Cannot say I have ever experienced this with my manual

 

[_olllllllo_]

IDK if on sport, but there is a setting for maintaining revs when shifting and also a rollback prevention setting.

Try those.

I will have to look for the maintaining revs when shifting setting. I noticed that the engine revs freely and it took a little time to synchronize my shifts to let off the throttle immediately before engaging the clutch pedal. I have heard of other posters mentioning that Tazer may be able to help with this, but I haven't purchased a Tazer yet.

I turned Hill Assist off after getting inconsistent feel during launches and I believe the brakes may not disengage consistently. This is a touchy topic as others have experienced the same improvement in clutch feel at launch and others don't experience a difference. I will not use hill assist and for the second 20,000 miles my manual has been more pleasant to drive.

My JLUR seems to rev closer to 1500 rpm on cold start (and I live in Southern Arizona so that may be in the low 40˚ range as the worst most of the time). I usually allow the coolant temp to reach between 75˚ - 80˚ when the engine rpm's begin dropping below 1000.

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