I'm working on a 08 C6 base 6.2, that has me lost been chasing this issue for cpl weeks read every post I could find with no resolution. Car ran and idled decent before the latest addition of the ported TB and intake, car currently drives and runs really good and it idles almost perfectly around 925 rpm (could go lower but owner requested lil higher idle) in open loop and for a short period of time in closed loop then jumps up 4-500rpm ,can turn car off and restart and it'll idle fine for 5-10 seconds then jumps up 4-500rpm. pulls max timing, maxes out stft, tps bottoms out. If u command open loop w scanner it goes back to within 100 rpm. Tried every idle guide, tip and suggestion I could find or think of, car likes airflow around 12-14 g/s and timing around 16-18 everything seems fine until it gets into closed loop idle, played with all the adaptives tried tuning the o2s. After getting the maf dialed in reasonably close have it running good ,maf only to eliminate the VE interaction. No changes seems like nothing I do changes anything about the fault conditions. Thanks in advance for any help.
Car has a mild cam (don't know the specs) aluminum flywheel lightweight clutch assembly, under drive pulley ported rod-mod intake, ported TB, kooks 1-7/8 longtubes 3 inch X pipe high flow cats.