I have a 2010 Cobalt SS with stock internals / turbo / full bolt-ons tuned by a local. The car was initially tuned on a dyno and making about 300 whp at 22 - 23 PSI.
The STFT is showing very brief spikes to rich and lean conditions, -20 to +20. These are very brief, to the point that they don't show up in HP Tuners when too many PIDs are being logged (because of the reduced logging frequency).
From what I can tell, it spikes lean when I'm coming in and out of DFCO. While it would spike rich when I'm braking in gear.
My car drives wonderfully. There's no KR, other than mild tip in knock that never goes beyond 5 degrees. My LTFTs are between -2 to +2.
The tuner is well respected in Ontario, and I trust that he knows his stuff. This is an oddball problem he's never seen before. We tried smoothing out the cam tables today but that did not help. Can anybody offer thoughts as to what is going on? Thanks.