Stumble, stall or rpm fluctuation on idle when cold outside

[Ben1029]

When it’s cold outside (20 degrees or colder) the truck starts and idles normally, but once engine temp gets to normal temp then  I come to a stop or slow down below 5mph the rpm’s surge/ or change and sometimes stall out. Once it stalls you hear a pop noise. I can raise rpm’s then it goes away but it will come back again. Truck has been to dealer 2 times already and they say it normal but I don’t think so. Not sure what to do because it’s getting annoying

-changed spark plugs at 48,000 miles

-transmission fluid was changed 45,000

- new air and cabin filter

- run 89 octane fuel 

[Bikerjon]

15 hours ago, Ben1029 said:

When it’s cold outside (20 degrees or colder) the truck starts and idles normally, but once engine temp gets to normal temp then  I come to a stop or slow down below 5mph the rpm’s surge/ or change and sometimes stall out. Once it stalls you hear a pop noise. I can raise rpm’s then it goes away but it will come back again. Truck has been to dealer 2 times already and they say it normal but I don’t think so. Not sure what to do because it’s getting annoying

-changed spark plugs at 48,000 miles

-transmission fluid was changed 45,000

- new air and cabin filter

- run 89 octane fuel 

Not normal. The engine should not stall or misfire. Has anyone scanned this truck for codes with a proper scan tool?

[Ben1029]

Yes, this truck has been to dealer 3 times and they say it’s normal. There are no codes or anything in system. We cleaned MAF sensor, replaced all filters and even throttle body cleaned but issue still happens randomly 

[Silverado4x4]

Did this start after plug change these motors are very sensitive to aftermarket or non OEM spark plugs. Did you put the exact OEM plugs back in? Amazon and some auto part stores are notorious for selling OEM knock offs. Check the connection to the spark plug from the boot could be loose make sure you feel the click. The problem your describing aftermarket plugs can cause this. Check to see if the new plugs are cracked very easy to do on the install.

Edited February 20, 2025 by Silverado4x4

[Ben1029]

The plugs were bought at GMC with OEM plugs and I installed them . I will inspect plugs but if the ceramic on plug is cracked it more would have misfire under load. Not saying it can’t happen at idle but it would happen more under strain or load on engine 

[silveradosid]

you are going to have to hook up to a good scanner that can monitor all the sensors. when it happens something is not right and there is many things that can cause this to happen

[Ben1029]

12 hours ago, silveradosid said:

you are going to have to hook up to a good scanner that can monitor all the sensors. when it happens something is not right and there is many things that can cause this to happen

I do have a solus plus scan tool I use but it’s hard to figure out what’s going on be I only have limited time from when it happens.
I do know when GMC removed my intake for warranty work they pinched #2 ignition coil wires and taped them up because they said they were still connected. but I still have no misfires on any cylinders. I’m wondering now if the #2 coil wires that were pinched are causing issue even though it may not be a big enough misfire to detect?

[Ben1029]

I did look at plugs and none are cracked as I can see

[silveradosid]

does it have any codes , light might not be on but there could be pending codes

[Ben1029]

No codes, no pending codes and no lights on 

[Ben1029]

Found and fixed issue 

PCV line fitting was cracked on intake causing stumbling idle and stalling. Brought truck to dealer and told them to keep truck until fixed and got rental car for 4 1/2 weeks just for a PCV line. No issues now for 3 full weeks. 

[davester]

thanks for following up.