idle surge/fluctuation 6.0L

[Paul Nelson]

I have a new-to-me 2011 GMC Yukon XL 2500 6.0L w/ 23K miles on it. The car runs great and is idling around 500 RPM, but every minute or so it will surge (slightly lower then slightly higher +- 50-100 RPMS) to the point where you can feel it in the steering wheel and overall the car surges. It isn't to the point where the engine feels like it will dies, but more like the idle drops and then the computer compensates. It will do this both when in P or while in D at a light. It seems to be less of an issue when the A/C is off and my observation with the hood popped is that it does seem to correlate with when the A/C compressor engaging (climate control on auto).

I found a couple threads on here about this, but they were inconclusive. I also ventured onto some other GM related forums and it seems this is a commonly brought up topic. Some say it is just normal for the 6.0L due to how low they idle in an attempt to save on fuel while others talk about TB and MAF cleaning. There is also mention then customer tuners such as HPTuners can be used to smooth out the idle.

I am debating taking my Yukon to the dealer and seeing if there isn't an ECU software upgrade and just to have them check it out. I still have a powertrain warranty (not likely to cover this) and a 3rd party warranty with $50 deductible.

I would appreciate any thoughts on this.

Thanks,

Paul

 

[AZSCTACO]

Mine did this as well and searched and searched. I had the Alternator checked a couple of times and they said it was ok. I didn't believe it cause I would get this fluctuating idle like you describe.....more when there was a load on the engine like the a/c was on....fans were on. Anyways.....I replaced the factory 145amp alternator with the HD 160amp alternator and its perfect now. I came to the conclusion the alternator was either not providing enough amps near idle or the voltage regulator thats built in was going bad. Any other symptoms your truck showing?? Like flickering interior lights?.....a/c interior fan speed sort of fluctuating?

 

[Paul Nelson]

Thanks for the reply AZSCTACO! I have not noticed any light flickering or A/C interior fan speed fluctuations, but I will pay closer attention to that. What I have noticed is that if I turn off the A/C it does not seem to do it (at least not in the few mins I was paying attention). It was in the low 100s this weekend and I noticed that the idle was around 600RPMs when the A/C was on high with front/rear cranking. I am not sure if this is normal or not.