2020 with slight vibration at idle

[Nutro]

2020 Tahoe with 167K miles. Its a former Texas DPS unit but the records show it had a LOT of service/maintenance and new transmission recently. It had the transmission tuned with ZL1 torque converter and DFM tuned out. New GM motor mounts in the last 2 years.
Fresh oil change and oil catch can and a can of fuel injector cleaner.
It has a slight miss at idle and when you drive it then put it in park, the idle climbs to around 900 then back down a few times.
Runs great, no noises at all. No check engine light etc.
Any idea on the idle surging a little and a slight vibration at idle?

 

[tom3]

Vibration at idle could be a slight imbalance of the torque converter or some flex plate runout. At that mileage the valves could be sludged up on the back sides and disturbing the air flow at the low speed.

 

[Jake707]

Is the truck new to you? I read that these have such a low idle speed from factory for EPA that it feels like a miss fire. Our 17 has a slight "miss" while idling however I have had it hooked to a scanner and no miss fires were reported and plugs and wires are new. Apparently raising the idle just a 100 or two RPMs is a common addition when tuning to smooth it out. Could be what you are experiencing


Surging is usually contributed to an air intake leak of some sort, vacuum line, intake seals etc. Spraying brake cleaner around the intake manifold area while running is easiest way to check for air leaks.

 

[persistent]

any time there are misfires, you should get a scan tool and check the dtcs.

when i was having regular misfires on 1 cylinder, the ecm would increase the timing advance until it would drop back to zero and repeat. it created a sawtooth pattern for engine rpm, where it would surge up to 700 then drop back to 450 and repeat. once i fixed the cause of the misfire, this sawtooth pattern for idle rpm and timing advance stopped.