I have a 2009 Yukon Denali with the 6.2l and it ran smooth until 80,000. miles. I replaced 8-coils, wires, spark pluges and the TPS along with the sensor on top of the TBI unit. It still have a rough idle. On the Tech 2 no codes or miss fires show up. I run 89 and 92 octane gas from BP or Shell. Dealer changed the cam position sensor and that did not do anything but cost me $300. Checked for air/vacuum leaks and found none.
Weeks went by and two o2 sensors were replaced and still a rough idle. All this time it wound up being a fuel injector sticking and injector cleaner could not fix it so I had to tie up the vehicle for two days while I went through each injector one by one until I found the faulty injector.
Now my 6.2 runs smooth and quiet, I sometimes forget the motor is running.
