at4 with 6.2 rough idle

[cbprov]

my 6.2 in my at4 runs rough at idle any body else have this or is this normal for the engine as it cuts out cylinders

[OnTheReel]

They only run in v8 mode at idle, no cylinder deactivation. I’ve noticed mine will sometimes idle rough after an “auto stop” restart but not otherwise.

[truck_newbie]

I suspect it might be from the flappers closing and opening due to the exhaust gas pressure being low. I noticed something similar in mine with the factory exhaust. I'm not experiencing it anymore with the cat-back exhaust. 

[fatwhiteboy]

Mine does it once in a while and it is annoying but I do not want to take it back just for that.  I read to run some premium gas in it.  The 6.2L engines love higher octane gasoline.  I am on my third tank of Sunoco 93 octane.  I can say it is better but still hick ups once in a while.  BUT on the good side I am seeing the best fuel mileage since I bought the truck, generally over 20MPG on the highway at 75 - 80MPH.

[Rocky Mountain At4]

My 2020 at4 with 6.2l idles rough too. I only feed it premium gas, but it definitely seems unhappy at idle.

[aliveguy5]

I think the idle could use about a 50-75 RPM bump. 

[Sammytheo]

I have a 2020 GMC Sierra with the 6.2L and its also been idling rough.  I notice it after the dreaded auto stop feature starts the engine.  Not sure what is the issue but I can tell its rough.  I have about 5.900 km on the truck and it started to run rough at idle about 1500km's ago.  At that time I also noticed that when starting it up after it has been sitting overnight I get a puff of blue smoke when I remote start it.  I figured it was the valve guides but hoped it wasn't the piston rings as a worst case scenario.    When I took it into the dealer they diagnosed it was bad valve guides.  I am waiting for the new guides to be shipped in from the US which could take a month because of the pandemic.  Having said that, the problem could be  fouled spark plug because of the oil burning off after I do a cold start.   Use the remote start and stand behind the truck when it starts up and see if you get the blue smoke when you do a cold start in the morning.  The dealer without hesitation said they would replace all the guides on both heads just to be safe.  If you are having a similar problem and the dealer tells you its your valve guides make sure you get all of the guides changed not just the one or two that are leaking.  I am also going to have the spark plug changes in the cylinder that is the issue.

 

Good luck

ST

[Sammytheo]

Now that gas is cheap I run 94 octane in Canada. I was using 91 and 89 octane in my 6.2L Sierra. I didnt notice any change.

[Rcfire]

On 9/22/2019 at 12:05 PM, cbprov said:

my 6.2 in my at4 runs rough at idle any body else have this or is this normal for the engine as it cuts out cylinders

I have a 2021 Silverado with the 6.2 and mine indies rough.  Had it in the shop twice and they say everything is good.  So frustrating 

[Rcfire]

On 9/22/2019 at 12:05 PM, cbprov said:

my 6.2 in my at4 runs rough at idle any body else have this or is this normal for the engine as it cuts out cylinders

Mine is the same way.  It idles terribly almost like it’s gonna die or a misfire.  Had it in the shop twice and they says it’s normal. Love the truck but seriously thinking of getting rid of it because it drives me crazy.  Come on GM !!’ This is terrible… it’s 2021 lol you would think a brand new truck would idle smooth 

[Kilgore Trout]

My 6.2L AT4 idles normally, quite smooth (oct 2021 build).  

 

I don't have auto-start/stop, so my engine stays on until I shut it off.