First post:

" No codes hidden or shown. According to him sensor readouts were there and seemed proper. "

Hard to believe the O2 readings were ok.....and that an O2 code was not set.....

I agree, I'm drawing a blank. Without a scanner I'm flying blind and taking their word for it. At this point I'm going to try an O2 since its the original and the car has about 140k. If this doesn't fix it, i'm driving without it plugged in. At least until I can find time to drop it off at a dealer and say "you fix".

Wanted to close this out. Just incase anyone else has a similar problem. I got around to replacing the upstream O2 sensor today. Runs great. Still not sure how that'* possible but whatever, it runs.