2018 Silverado Spark Advance Issue

[portert]

Like many, I'm very new to tuning via software. I'm taking it slow and easy. My problem is the L83 suddenly has developed a stumbling idle and even if i accelerate quickly. One thing i notice which is bothering me is the spark advance jumps all over the place at idle while watching the scanner. It'll go from like 2 to 41 and all parts in between at idle. Leave a steady, close knit zig zag pattern on the graph. The idle bumps and sputters and might smooth out momentarily, This is a 100% stock L83 with 69,000 miles on it.
I was thinking along the lines of:
A worn or broken timing chain tensioner
Weak coils starting to break down
Possibly a sensor or 2 breaking down.
I don't get any DTC codes. The engine overall seems sluggish although starts right up and under light load, runs pretty well. I have disabled the DoD feature through the VCM Editor. If anyone has any ideas on this issue your input will be greatly appreciated. I leave in Phoenix, AZ and driving in traffic with 3.08 gears, I'm wanting to switch to a 3.42 ration but i want it to run right first.
THanks

[GHuggins]

Start by doing an induction clean. Run a can of foaming gm top engine then a can of sea foam then repeat while easing in and out of throttle sitting still. Youtube how to do an induction clean to get the gist of it. You'll have to unplug and fire it up with the MAF unplugged. Run 4 cans through - yes it's pricey, but works then see if that made any difference. Really sounds like your intake valves are clogging up. I have also see injectors start sludging and sticking cause the same problem.

[DustinG]

Follow what Greg said - DI engines are very prone to carbon and can cause a lot of issues. I would also log misfires and other pertinent info and post the file so folks can help identify what might be going on.