2018 Silverado 6.0 Idle Stumble

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May 1, 2012
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Indiana
2018 Silverado 3500HD with 6.0L gas motor.

I notice in the morning when I start my truck, the idle stumbles moderately. As I back up out of the driveway, it stumbles as well as I pull way down the road. It immediately goes away once I get the RPM's up and is hardly noticable once warmed up and back in park.

The truck has never had a "sewing machine" idle. It's always felt a bit "rough". The tach has a small bounce to it (tiny), but you can feel it in the seat.... Even when fully warmed up.

Any ideas??
 
It's funny because my 2018 Elantra used to behave similarly. Turned out to be a bad coil, taken care of under warranty. Not saying that's your problem, too, as many things can cause a lumpy idle.

Are you still under warranty?
 
Yes, still under warranty. No CEL. I always get good gas, it has done this for 2 years, 45k miles
 
It would be interesting to do some data trends on it to see if it is misfiring at idle.

Apparently it's not enough to light the CEL.

Could be nothing.
 
Why even speculate or worry about it. Take it to the dealer since it's under warranty and let them diagnose and repair it. Make sure you tell them it stumbles the worst in the morning when cold.
 
Originally Posted by JTK
It would be interesting to do some data trends on it to see if it is misfiring at idle.

Apparently it's not enough to light the CEL.

Could be nothing.


Nothing? If it won't idle correctly it has a problem.
 
Originally Posted by PowerSurge
Why even speculate or worry about it. Take it to the dealer since it's under warranty and let them diagnose and repair it. Make sure you tell them it stumbles the worst in the morning when cold.


I've tried it. Two differrent dealerships basically said, "We've had a few people mention this. We've looked into it. There's no CEL."

I guess I could take the truck to a "tune shop" and have them obtain some data. Perhaps some fuel tables need adjusted.

Anyone have any other ideas?
 
Originally Posted by Phishin
2018 Silverado 3500HD with 6.0L gas motor.

I notice in the morning when I start my truck, the idle stumbles moderately. As I back up out of the driveway, it stumbles as well as I pull way down the road. It immediately goes away once I get the RPM's up and is hardly noticable once warmed up and back in park.

The truck has never had a "sewing machine" idle. It's always felt a bit "rough". The tach has a small bounce to it (tiny), but you can feel it in the seat.... Even when fully warmed up.

Any ideas??


If they can't locate the problem and it bugs you every day, trade the vehicle or sell it.

I once had a new early 70s Ford Econo Van that had loose steering that drifted, direction depended on road slant. Never got fixed despite complaints by me. By the time it was a year old, I got fed up and traded-it-in.

Never bought another Ford again. My first car-ever, in 1969, was a Ford. That was a bad decision purchase. Me and Fords don't get along.
 
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Tried a strong dose of PEA based fuel system cleaner … ?
Two bottles of Gumout Regane just cured rough idle in my 5.3L
 
Originally Posted by 4WD
Tried a strong dose of PEA based fuel system cleaner … ?
Two bottles of Gumout Regane just cured rough idle in my 5.3L


Yep. I've run 2x doses for 2 full tanks. I've also run a few tanks of E85 through it. (It's a Flex Fuel compatible 6.0L)
 
Lot of parts houses can plug in and look for codes that will not always trigger a CEL on the dash. Free service.
 
You have any video of this? What gas are you running? Have tried an actual ECM reset?
 
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You have any video of this? What gas are you running? Have tried an actual ECM reset?

It's something that would be hard to capture on video, really. I'm running Shell or Sunoco 87 Octane fuel. No, I haven't tried ECU reset.
I had the GM dealer scan for codes, and they saw nothing.

Like I mentioned before, in the morning, she just stumbles a bit at start up....maybe 30 seconds or so. You can feel it as you put it in gear and move the truck. It is NOT bucking and jumping around, but you can definitely feel it. Kinda similar when you start up an older piece of power equipment (like a garden tractor or even a weed eater....you have to let it warm up a minute before it's really going to run smooth.

I've tried to get it to "stall"...but it won't. If I give it a decent amount of fuel right at start up, it hesitates and grumpily begins to accelerate....and of course, smooths out very quickly.
 
Personally, every GM LS engine I have owned or experienced runs a bit rough for the first 30 seconds or so. I'm not sure I would say it is a "miss", but certainly a bit rougher, with maybe even a bit of a "lope". After they warm up for a few seconds, they seem to settle in nicely.
 
My elantra just had a coil replaced under warranty. It was skipping at 1800rpm in top gear. No cel, and not dtc on my hand held code reader.
 
And this is the problem with computer diagnostics. If it does not set a code the dealer does not want to deal with it even though there are a ton of sensor read outs that will tell you if something is going wrong. But you have to know what the normal reading should be and how to run the tests which is either beyond most techs or not profitable.
I have a similar problem with my 2015 3500 Express. Occasionally I get a slow start where I turn the key and it takes a few sec before the engine starts to crank and then everything goes back to normal the next 50 starts. I always go to ON for a sec or 2 to let the fuel pump run before going to start but it does not help and the dealer tells me the same thing, No Code No Problem. And I also have the rough Idle for 30 or 40 sec on cold starts.
 
Direct injection? If so, welcome to the GM truck misfire club! I was a member, along with several others (you can find us at the GM trucks forums).

You have several options...
Take it to the dealer, they won’t cover it under warranty (seeing how it’s out of bumper to bumper). They’ll hit you with a diagnosis fee and try to find the problem. If it’s a misfire they’ll tell you “normal”. And that’s ok because basically nothing is covered under the drive train warranty except mechanical parts, not injectors or coils. Nope. And that’s ok because the injectors are on back order, you can’t get them.
Your other option is to trade the truck in, like many of us already have, before you really run into problems, like collapsed lifters and failed transmissions.

However if your engine is just a regular port injected, no cylinder deactivation engine. You’re good! That’s just the good old GM stumble bumble.
 
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