2021 3.0L RST Skipping and rough when cold

Santito · February 2, 2025

Got a 2021 3.0L with just under 30k miles and recently started acting like it was misfiring or skipping while in gear and brakes on. Noticed it would happen while stopped or just starting to take off and would occur within a few miles of starting my trip and wouldn't matter if I had preheated the truck. Now, especially that the outside temp is in the single digits it's happening more. No codes, no check engine light. I had it in for an oil change and reported it then but of course the dealer couldn't reproduce the issue. Today it's been doing it more than normal and was able to get it on video... But still no codes. Once it's over 1k-1.5k RPMs it's clear and after I driver for at least 5 miles it won't do it until it cools back down.

Have not found much on line about it nor other reports.. can't find anything disconnected, broken or damaged under the hood as far as vacuum lines, connections and even the air box assembly.

Any other reports of this?

Santito · February 9, 2025

I can't be the only one that's had this happen. Skips like it's miss firing or maybe an injector acting up. The frustrating part aside from no codes is it doesn't happen all the time even on the cold days.

silveradosid · February 9, 2025

you should still get it scanned to see if there is any miss fires on any of the cylinders

Santito · February 9, 2025

8 hours ago, silveradosid said:

you should still get it scanned to see if there is any miss fires on any of the cylinders

Last time I reported it to the dealer they claimed there was no info when they scanned it.

redwngr · February 11, 2025

Try pushing the onstar button when it's doing it and see if they can catch the code.

Santito · February 13, 2025

OnStar is a sore subject... But no service with them.

Got my hands on a code reader and plugged it in .... All clean and no codes and it did it as I left work for the day. It seems to definitely not happen after the engine reaches 185 degrees and up to operating temp. If it is happening and I can get the RPMs over 1,500 it clears out but once I let it get back to idle it will happen until the temp comes up. Another thing I noticed is that it typically idles at about 750. When it starts acting up and it's idling smooth it's more at 850-900.

Santito · March 1, 2025

So far the only other info I've been able to determine that this occured when the engine temp is about 185 or less and the ambient air temp is around 40 or less and the RPMs are slightly higher. Air\Fuel mixture or cold air intake issue possibly while the choke or choke mode is on??

KinkyDuramax · March 2, 2025

If you have no codes, or past codes - Just drive it until it comes on. I don't have that issue though. When the windchill was -20F, around 0F I had the engine block heater plugged in for a few hours. Started right up. But never had any of the issues your describing. Same motor.

Santito · March 3, 2025

Yea it's been driving me nuts with no codes and we are now going on almost 3 months of it acting daily now. I have had it stall out on me a couple of times recently and the symptoms just keep getting more pronounced. Hopefully it Will throw a code or error soon!

GMCustomerService · March 5, 2025

On 3/2/2025 at 8:55 PM, Santito said:

Yea it's been driving me nuts with no codes and we are now going on almost 3 months of it acting daily now. I have had it stall out on me a couple of times recently and the symptoms just keep getting more pronounced. Hopefully it Will throw a code or error soon!

We want to learn more and make sure we get the appropriate parties involved. Please send an email to [email protected] with your VIN, along with a history of your vehicle concerns. Please be sure to include "GMC Trucks Forum" in the subject line. By sending us a message, you consent to the information you provide being monitored and recorded by GM or those acting on GM’s behalf, subject to the GM Privacy Statement: https://www.gm.com/privacy-statement.

Santito · March 9, 2025

On 3/5/2025 at 6:51 PM, GMCustomerService said:

We want to learn more and make sure we get the appropriate parties involved. Please send an email to [email protected] with your VIN, along with a history of your vehicle concerns. Please be sure to include "GMC Trucks Forum" in the subject line. By sending us a message, you consent to the information you provide being monitored and recorded by GM or those acting on GM’s behalf, subject to the GM Privacy Statement: https://www.gm.com/privacy-statement.

Email has been sent.

GMCustomerService · March 9, 2025

16 hours ago, Santito said:

Email has been sent.

Thank you, we will be in touch soon.

Santito · March 29, 2025

Well the mystery has been solved. It was found that the when the air filter was inspected at the last service, the hose was not connected to the air box correctly there was an air leak going by the mass airflow sensor. Couldn't see it from the front side of the engine.....

Edited March 29, 2025 by Santito