'07 Avalanche "System too Lean" CEL

Hi all,
Long time since I posted anything, but this is weird. I cleaned & oiled my Injen air filter over the weekend, after running about 45K on it, and restored my Av back to stock tune. I wanted to get the LTFT's in stock mode, just to see the difference between it and the DiabLEW tune I run. I dorve it about 15 miles this morning, and the CEL comes on, with the System Too Lean code for both banks. It was at +39! I cleared the code, and ran the rest of the way into work in 3rd to keep it from running in 4cyl mode. I live 45 miles from the office, and by the time I got in, it was down to +19, but still, that scares me. Any ideas of what to check? Everything's tight, and no exhaust leaks, so I'm wondering if maybe too much oil on the air filter would cause this?

Thanks,
Brad

[mikel]

yup, likely got oil all over the MAF element.

Cleaned MAF, no change. Took it to shop, and they declared the MAF had gone south, so it was replaced. The fuel pressure test, while in the low-middle range, was rock-steady, so they said that was fine, and a vacuum leak at the plenum was taken care of. Idle is still rough, and it still seems to have fuel delivery trouble at part throttle as well as WOT. LTFT's are between +8 & +10 on the stock tune @ 2k rpm, with a CAI and dual exhaust. I know those two bolt-ons will move more air, leaning it out, but that still seems pretty high to me. I guess I want to get it taken care of with the stock tune in it before putting my DiabLew tune back in.

[mikel]

the CAI will likely cause the trims to move like that....

[06MonteSS]

yeah, sounds normal man, no issues...

Put the DiabLew tune back in Thursday night, and after ~100 miles, my LTFT's are back to normal, at -1.56 bank 1 & -.78 bank 2. Looks good, but still worried about the "stutter" it has when getting up to speed, as well as a huge tranny slip in the 3-4 shift. I'll be out of town next week for the holiday, so I'm leaving it at the dealer to diagnose the tranny. I've had issues with it from day 1, so even though I'm at 120k, the dealer is willing to work with me.