'05 Tahoe 5.3 / P0171 / Rough Idle / Misses

[taj1991]

If you have a lean mixture on both banks, I would first check all the related parts, regardless the cylinder heads.

And first I would check for air leaks, that is most likely, probably the intake assembly is not mounted correct, or they forgot a hose, for example from the PCV,

Additionally check the air mass sensor, very important check the fuel pressure and check the o2 sensors.

And you can measure the compression. If the compression is equal, the engine should have the same amount of air in the combustion chamber and should inject the correct quantity of fuel, so you should have a correct combustion.

Okay, all of that makes sense. I've got a smoke test scheduled, and I'll have the mechanics check those finer points also. Thanks for reply!