2007 GMC Yukon Denali 1500XL AWD
6.2L V8
187k miles


Been having some engine issues.
Replaced all 8 spark plugs, wires, coils.

Now at idle, no significant shaking.
Fuel System 1 and 2 status move to OL-Fault after a minute or so
Then traction control and stability lights come on
Followed by flashing check engine - P0300 multiple misfires

Check each cylinder report - 0 misfires on all

Get the RPMs to 2000 and the Fuel status 1 and 2 both go to CL.
The engine light goes away
The traction and stability lights go away

Drives fine. No noticeable issues other than the beeping an annoying flashing lights.

Issue seems to be air intake or fuel mix or sensors.

Short term fuel trim stays at 0.0% until the RPMs are up. Open loop fault?

O2 sensors seem sluggish - move between 0.9v and 0.2v.

MAF 0.78 to 0.83 pounds/min at idle
MAF 2.5 pounds/min at 2000 RPM

All the problems are at idle. I cleaned the throttle body, added fuel, did a battery reset. What else?

I threw all this into AI and it says I need to replace the front two O2 sensors. But what do humans think?

I'd look for a vacuum leak.

Have the intake manifold gaskets ever been replaced?

Moved thread from General GM Chat to GMC/Chevrolet Truck/SUV .

Thank you. Most likely not ever replaced.

It was a government fleet vehicle from 2007 to 2015.
My parents have owned it since... I'm trying to fix this for them.

Gotcha.

No guarantees, but with what you've described, that'* where I'd start to investigate first.