2015 GMC Yukon Denali idle issue in 6.2 liter engine

Z45 · August 5, 2016

No problem like this with mine in 23,000 miles. I always use premium fuel but I hear many say, don't need it. Are those with this issue using premium fuel all the time?

Rick J. Pagan · December 21, 2016

No problem like this with mine in 23,000 miles. I always use premium fuel but I hear many say, don't need it. Are those with this issue using premium fuel all the time?

I have a 2012 Yukon XL Denali. Have same problem, only that it got so bad I thought the car would stall out and the tranny would downshift hard. Bought it as CPO August 2016 w/49K. I use it for work so now it has 65K. Service records show prev. owner had injectors flushed at 28.5. Initially I was using E85, but at the behest of my dealer, I started using premium only. In fact, in the fuel door it says "Premium or E85 only." The dealer's explanation is that in order for the 6.2 engine to be fuel-efficient, GMC has had to design this engine to run very lean. The rough idle problem was much worse when using E85.

On the advise of my local auto parts, I removed the throttle body and cleaned it thoroughly, cleaning also the IAS sensor and the MAF sensor. Stalling problem solved, but rough idle persists, only less often. One thing that was very interesting, is that when I was getting ready to put the air intake piping back on, the inside was caked with oil, as was the IAS sensor.

My dealer recommended a GDIS service, which is supposed to clean the entire fuel delivery system including the injectors the throttlebody fuel lines and the tank. But, I'm not spending $400 without any guarantee the problem will be solved.

Edited December 21, 2016 by RJP62

truckguy82 · March 24, 2017

There's a "engine misfire on startup" CEL that requires fuel injector replacement, likely not the fuel injectors causing the rough idle issue though.

I think the problem is carbon buildup on the back of the valves.

If you never had a catch can, it'd probably be a good idea to get the valves cleaned and then install one anyway. If it doesn't resolve the idle issue, it's certainly not a waste of money.

Thomas Jancewicz · October 14, 2017

I have a 2009 Yukon Denali with the 6.2l and it ran smooth until 80,000. miles. I replaced 8-coils, wires, spark pluges and the TPS along with the sensor on top of the TBI unit. It still have a rough idle. On the Tech 2 no codes or miss fires show up. I run 89 and 92 octane gas from BP or Shell. Dealer changed the cam position sensor and that did not do anything but cost me $300. Checked for air/vacuum leaks and found none.

Weeks went by and two o2 sensors were replaced and still a rough idle. All this time it wound up being a fuel injector sticking and injector cleaner could not fix it so I had to tie up the vehicle for two days while I went through each injector one by one until I found the faulty injector.

Now my 6.2 runs smooth and quiet, I sometimes forget the motor is running.

bkyle17 · October 22, 2017

Just bought a new 2017 6.2L Sierra Denali 1500. It has a subtle rough idle. Thought it would resolve with premium fuel but no luck. Brought it to dealer but computer didn’t show any abnormalities. Also occasionally as I slow down the tranny seems to “catch” as it down shifts to first. Not sure if it’s realated to the rough idle. Any thoughts on either issue? Thanks!

Johnnyrt · May 30, 2019

On 10/22/2017 at 11:59 AM, bkyle17 said:

Just bought a new 2017 6.2L Sierra Denali 1500. It has a subtle rough idle. Thought it would resolve with premium fuel but no luck. Brought it to dealer but computer didn’t show any abnormalities. Also occasionally as I slow down the tranny seems to “catch” as it down shifts to first. Not sure if it’s realated to the rough idle. Any thoughts on either issue? Thanks!

I just got a 2018 w/ 30k miles, I have the same issues! The dealer told me this is "normal"

DreamCadi Can you please share the fix??

avalonandl · May 31, 2019

The 6.2 LT engine has an aggresive cam. It does not idle dead smooth like the LS engines. It is the same cam as the camaro SS so its a performance cam.

Johnnyrt · May 31, 2019

1 hour ago, avalonandl said:

The 6.2 LT engine has an aggresive cam. It does not idle dead smooth like the LS engines. It is the same cam as the camaro SS so its a performance cam.

I get that, I have a 73 C10 w/ a 383.... But this is not just the cam. I have driven many other 6.2's that do not have this issue. It's like every 3 or so seconds, the engine stumbles, you can even see the RPM needle on the gauges move.

avalonandl · June 2, 2019

Sounds like a air leak?

Bob2C · June 4, 2019

I have a 2018 Tahoe with 8k miles and have the same issue. Mine has a rough idle when warm and idles slightly below 500 RPM. I tried different gas stations of 87..What seemed to help was installing K&N filter and tightening the clamps for the intake hose. I also tightened the torx screws on the air flow sensor. They were very loose.. I am guessing there might be a vacuum leak somewhere. Its better but not perfect. Dealer said its normal operation.. Go figure

Johnnyrt · June 4, 2019

Two seafoam treatments and installing a catch can seems to have taken care of the shivering!

Frankdatank01 · August 20, 2019

I’ve replace both banks of injectors in 2016 Yukon 6.2L due to throwing code. When they put the one side of injectors back in, the idle still had a stubble. I was always told it was normal and figured as such but one of thier “heavy techs” did some more tests and it ended up being the cam/lifters. Those items were repaired under warranty. The injectors are not covered....sigh. Once the cam lifters were replaced, the 6.2 purrs.

if you can’t diagnose your idle stubble, look at cam/lifters or have your tech investigate.

videoarizona · August 26, 2019

Last March 2019, I bought my new to me 2015 Sierra Denali with 6.2. 60K miles. It was idling so bad the dealer replaced the engine mounts which didn't solve the problem. I realized the P.O. made many trips to Mexico...and knowing how bad Pemex gas is, I threw in some Techron and started using 91 octane top tier fuel. I also have been running Seafoam as well.

Now, after 10K miles and 2 trips towing 6Klb trailer...the premium gas and fuel cleaners have done the job. She starts without that huge shake, runs at idle smoothly with a little stumble now and then... and purrs at speeds. MPG's have gone up as well. Not using any cleaner now...just premium gas.

Bottom line? Clean the fuel system. The 6.2 can be silky smooth then...IMHO.

ArrowsmithPML · September 23, 2019

New Guy Alert!

After a lot of reading I have a 2017 Yukon Denali XL that has 41,000 km (not miles) on it and I've owned it new. I'm inside the 60,000 km 36m warranty so that's ok BUT...

Recently had injectors #2 and #6 replaced only after I bought my own Autometer Code Reader / Data Logger as the dealer said there was nothing wrong with this "intermittent idle shudder" I reported at about 35,000 km. So, displaying a P050D code and telling them from what I've found either this is an injector issue or a coolant issue on the block I need this looked at. Anyway, hence, the 2 injectors replaced. Now, 3 weeks later, same issue (but no code) and #8 replaced, took it home, the next day, same issue and you wouldn't think anything was done...

I later discover that injectors are a consumable per the warranty and won't be covered past the 60,000 limit! I've never had injector issues on any diesel and making the switch back to gas and I get this mess? Not really impressed.

So can someone tell a guy that knows enough to be dangerous but not much about GM products what is the numbering order on the cylinders per bank? I assume 2, 4, 6 and 8 on one side and 1, 3, 5 and 7 on the other but I could be wrong. My issue is that do I force the issue and get the remainder of the injectors replaced under warranty? Do I take it to a private shop and get this torn apart or do I trade it in for a 2019 which from what I can tell doesn't have any of this mess happening?

I've also got a 2018 Camaro 2SS with the 6.2L and it does not have any of these issues.