Rough Idle... not according to dealer

Rick Seagroves · February 28, 2018

My 2017 1500 Sierra Denali has had a rough idle since the 1st week of purchase. I thought it might need a "break-in" period, so didn't take it back to dealer initially. Rough idle has continued to the point that finally had to take it in. The dealer has finally noticed it as well, and agreed it is unacceptably excessive. Evidently GM has put out a bulletin regarding this issue, and the dealer replaced the motor mounts as per bulletin, under warranty. I asked about increasing idle RPM and mechanic said RPM is computer regulated and he can't increase the idle RPM. We all agree it has nothing to do with AC compressor kicking in/out, etc. The problem is intermittent, but has gotten worse, and is now somewhat consistent. It's to the point that all passengers in the truck notice it. 65 Grand for a new 2017 vehicle that idles noticeably rough? By the way, before 12,000 miles, had to replace starter, major water leak under dash, navigation screen (all functions) completely quit (black screen), transmission clunking on downshift.......I'm trading next week.....Has anyone noticed any similar issues with a Chevrolet Silverado?

wforrest08 · February 28, 2018

1 hour ago, Rick Seagroves said:

Has anyone noticed any similar issues with a Chevrolet Silverado?

Not to be a smart azz but have you read much on here? Besides the starter all these other issues have been discussed many multiple times both Silverados and Sierras. If your asking if you switch to a Silverado you won’t have any of these problems the answer is maybe maybe not will you have different problems maybe maybe not. It seems like to me anyway either you get a “good one” or a “bad one” a roll of the ? ? at best hopefully you don’t end up with snake eyes...

Just so you know idle can be adjusted with a tuner or a custom tune lot a guys have bumped it up 50 rpm to smooth it out. A tune also seems to help some of the tranny issues for some people at least with the 6 speed (like me) not sure about the 8 speed. Course you run into possible warranty issues once you do a tune, seems to depend on the dealer as to whether or not they want to work on it or not.

MikeNH · February 28, 2018

GMC and Chevy are largely the same truck underneath. You won't have any better or worse a chance of trouble with one over the other.

That said, this sounds like a lemon law case.

EChavez · February 28, 2018

I noticed a rougher idle on my 14. Truck would subtly vibrate, nothing violent but enough for me to notice. I swapped out the spark plug wires for msd racing wires. Been smooth ever since.

Rick Seagroves · March 1, 2018

As a follow up to my post regarding my 2017 1500 Denali with rough idle, I just received a call from the dealer. They said they did some code work, sent data to GM, and GMC is wanting them to replace transmission mounts. Seems they loosened trans mounts, idle vibration got worse, did a few other things and determined (GMC determined) it is the transmission mounts. They are doing that work tomorrow. Fingers crossed.....

Dr Awesome · March 28, 2018

On 3/1/2018 at 4:20 PM, Rick Seagroves said:

As a follow up to my post regarding my 2017 1500 Denali with rough idle, I just received a call from the dealer. They said they did some code work, sent data to GM, and GMC is wanting them to replace transmission mounts. Seems they loosened trans mounts, idle vibration got worse, did a few other things and determined (GMC determined) it is the transmission mounts. They are doing that work tomorrow. Fingers crossed.....

Did this help you out at all?

Rick Seagroves · March 28, 2018

Yes....and no. Rough idle is not as noticeable as before, but still noticeable. However, if you are the type that thinks an expensive truck, or any expensive vehicle for that matter, should perform at the level of an as advertised, top tier truck (GMC-Denali), than the answer is no. Bottom line is the engineering of the drive train, transmission mounts and/or engine mounts needs to be addressed to provide a decent idle. I think bottom line is that GMC does not have a solution for the issue. I will still consider a GMC for my next purchase, I will just research issues before I purchase.

qwank · March 28, 2018

Gm started putting in redesigned motor mounts in late 2016/early 2017 to HELP with the rough idle feel. Notice I said help, it doesn't completely eliminate the problem