Rick J. Pagan

I have a 2012 Yukon XL Denali. Have same problem, only that it got so bad I thought the car would stall out and the tranny would downshift hard. Bought it as CPO August 2016 w/49K. I use it for work so now it has 65K. Service records show prev. owner had injectors flushed at 28.5. Initially I was using E85, but at the behest of my dealer, I started using premium only. In fact, in the fuel door it says "Premium or E85 only." The dealer's explanation is that in order for the 6.2 engine to be fuel-efficient, GMC has had to design this engine to run very lean. The rough idle problem was much worse when using E85. On the advise of my local auto parts, I removed the throttle body and cleaned it thoroughly, cleaning also the IAS sensor and the MAF sensor. Stalling problem solved, but rough idle persists, only less often. One thing that was very interesting, is that when I was getting ready to put the air intake piping back on, the inside was caked with oil, as was the IAS sensor. My dealer recommended a GDIS service, which is supposed to clean the entire fuel delivery system including the injectors the throttlebody fuel lines and the tank. But, I'm not spending $400 without any guarantee the problem will be solved.