5.3l slight stumbling

[Teamwieland]

2013 Yukon XL 5.3l with 155k. Engine has had a slight stumbling recently that I only notice at idle. This week motor went in to reduced engine power mode and wouldn’t go over 15-20 mph. My basic scanner showed Throttle Position Sensor code. I just so happened to have a Trailblazer SS TB laying around and swapped that out. Did spark plugs as well since they were original. Now engine has a more noticeable stumble/miss that I notice at idle and while driving. No CEL, no codes. I don’t notice a lack of power, just feels like a constant miss throughout the rpm range. Not terrible, more annoying, but surprised it is not throwing a code.

 

[Fless]

Would your scanner show individual cylinder misfires? Wonder what that would show, if any. Might help narrow down what's causing the feeling.

 

[Teamwieland]

It does show individual cylinders but no misfires according to scanner

 

[tom3]

I wonder if a dose of good injector cleaner in the gas tank might help this deal?

 

[Teamwieland]

Did that before my 6 hr trip. I just tested fuel pressure and it is a tad low, about 53 PSI. My understanding is fuel pressure should be 55-60 PSI. Will look into that next

 

[Teamwieland]

Turned out to be a cracked spark plug. I replaced mass airflow, sensor, intake, manifold, gaskets, plugs, wires and a few other things. When I replaced throttle body I also did plugs and assumed it couldn’t be plugs. Wouldn’t throw a code or CEL so took to a shop today. Idles perfectly now.