Rough idle when 4H auto is engaged

[jy86206]

I found yesterday that the idle is more rough when 4H auto is engaged and the transmission is in drive, I could feel the vibration from seat while waiting for red lights, and the vibration disappeared if I shift it back to 2H. After driving in 4H auto for few miles the vibration disappeared even at idle. AC was on all the time. Has anybody seen this?

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[tengg2001]

Have you figured out? I just found it’s vibrating at 4h while waiting at red light.

 

[Dyolfknip74]

Have you figured out? I just found it’s vibrating at 4h while waiting at red light.

I'd say that is a front drive shaft issue.

 

[mwilk012]

I'd say that is a front drive shaft issue.

It’s not turning.

 

[Dyolfknip74]

It’s not turning.

In 4 hi the front drive shaft isn't turning?

Edit: just saw the "at a red light" part. I'm stumped. Lol

 

[AFD]

Bump. Same thing happening here.

Was originally thinking it was just an occasional rough idle after a 45-min trip home from work, but finally realized this was only happening if I had 4-auto or 4-high engaged. Mostly just a more pronounced vibration felt in the steering wheel and center console armrest that usual.

Everything seems fine while driving around in 4-auto or 4-high, but the vibration becomes noticeable once stopped while still in drive and even a little more pronounced once shifted into park. Shifting back into 2WD while parked doesn't seem to make it go away, but once driving again the next day, the rough idle issue goes away.

Just wondering how 'normal' this is supposed to be, if it's indicative of an actual problem (or nothing to worry about) and mechanically, what would be causing it?

 

[Maverickxeo]

I found yesterday that the idle is more rough when 4H auto is engaged and the transmission is in drive, I could feel the vibration from seat while waiting for red lights, and the vibration disappeared if I shift it back to 2H. After driving in 4H auto for few miles the vibration disappeared even at idle. AC was on all the time. Has anybody seen this?

I had this 'problem' in another vehicle in 4H (auto or locked) as well as in my JL 4H (locked).

There was a thread here that basically said it was normal because of the way an automatic transmission works. I'll try to find it for you.

EDIT: Here is the post: https://www.jlwranglerforums.com/fo...in-4h-when-jeep-stationary.84831/post-1946870

 

[jy86206]

Thanks for the thread. Yes, the rough idle is just there, no more mechanical problem. I guess it’s just a Jeep thing.

 

[blink9cd]

Thanks for making this thread, was at least hoping I wasn't the first one for this...been paranoid ever since I had the 2.0T overheating issue.

The other day I was driving in a lot of rain so I took it out of 2H and put it in 4A. At every stop light I noticed a significantly rougher idle than before...you can hear and feel it. Switching to 4H at the light did nothing, but switching to 2H made it immediately quiet down. If I then stuck it back in 4A/4H the rough idle did *not* come back for the duration of the stop. However, once I got to another light, the same rough idle came back, I could change it by shifting, etc.

No issues at all while driving. '21 with 2.0T /4A / LSD.

 

[Dyolfknip74]

Thanks for making this thread, was at least hoping I wasn't the first one for this...been paranoid ever since I had the 2.0T overheating issue.

The other day I was driving in a lot of rain so I took it out of 2H and put it in 4A. At every stop light I noticed a significantly rougher idle than before...you can hear and feel it. Switching to 4H at the light did nothing, but switching to 2H made it immediately quiet down. If I then stuck it back in 4A/4H the rough idle did *not* come back for the duration of the stop. However, once I got to another light, the same rough idle came back, I could change it by shifting, etc.

No issues at all while driving. '21 with 2.0T /4A / LSD.

That's very odd. Being in 4A at a stop light shouldn't be any different than being in 2wd. I'd get dealer to check it not.

 

[blink9cd]

That's very odd. Being in 4A at a stop light shouldn't be any different than being in 2wd. I'd get dealer to check it not.

I do have a Wave oil change coming over soon, does seem worth bringing up at least. It seems like a couple others in thread also have that issue, including when shifting out into 2H, but unfortunately never seen a clear diagnosis. Isn't one of the main differences in normal driving of 2H vs 4A that the FAD has to be engaged so power can go to the front if needed?

 

[Dyolfknip74]

I do have a Wave oil change coming over soon, does seem worth bringing up at least. It seems like a couple others in thread also have that issue, including when shifting out into 2H, but unfortunately never seen a clear diagnosis. Isn't one of the main differences in normal driving of 2H vs 4A that the FAD has to be engaged so power can go to the front if needed?

The FAD doesn't really have anything to do with the 4A setting (maybe, see below) . The FAD is only to stop the front drive shaft from spinning all the time. All JLs have that "feature"
Your tcase is what will automatically put you into 4h when it feels slippage in the front. That's why I'm saying it shoudnt be doing anything in 2H at a stop.

Now, what I'm not sure about is whether putting it into 4A will engage the FAD. But even if it does, at a stop,the DS isn't spinning anyway.

So, I with all that, I really don't have a clue why you would get NHV at stops. Lol. Sorry man.

 

[blink9cd]

The FAD doesn't really have anything to do with the 4A setting (maybe, see below) . The FAD is only to stop the front drive shaft from spinning all the time. All JLs have that "feature"
Your tcase is what will automatically put you into 4h when it feels slippage in the front. That's why I'm saying it shoudnt be doing anything in 2H at a stop.

Now, what I'm not sure about is whether putting it into 4A will engage the FAD. But even if it does, at a stop,the DS isn't spinning anyway.

So, I with all that, I really don't have a clue why you would get NHV at stops. Lol. Sorry man.

Yeah I didn't think it had much to do with 4A itself, cause at least from the other thread that was linked above, seems like there are others having this issue when in 4H. But was wondering what aspect of 4H that 4A also has but 2H doesn't, especially at idle...

Not saying it's the issue, I just figured the FAD was one of the main differences between 2H and 4A, as it would have to be engaged during 4A since you'd need to be able to power the front wheels. I don't think it does it dynamically in 4A after I saw this in the manual:

I should probably capture some screenshots of my tachometer for the eventual dealer visit. Maybe even a video if it could capture the "feel" of the increased idle.

 

[four low]

Thanks for making this thread, was at least hoping I wasn't the first one for this...been paranoid ever since I had the 2.0T overheating issue.

The other day I was driving in a lot of rain so I took it out of 2H and put it in 4A. At every stop light I noticed a significantly rougher idle than before...you can hear and feel it. Switching to 4H at the light did nothing, but switching to 2H made it immediately quiet down. If I then stuck it back in 4A/4H the rough idle did *not* come back for the duration of the stop. However, once I got to another light, the same rough idle came back, I could change it by shifting, etc.

No issues at all while driving. '21 with 2.0T /4A / LSD.

Maybe looking at the attached link in post #7 will explain this this benign behaviour for those noticing it.

 

[blink9cd]

Maybe looking at the attached link in post #7 will explain this this benign behaviour for those noticing it.

I did read that post and watch the accompanying video. While I found it informative, I don't feel super convinced it's nothing yet, especially in the case of 4A (unless someone has a lot more detail on what happens in 4A at idle), and why it's not happening to everyone (or potentially so few people, given the lack of engagement on these and related posts).

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