Unbelievable. The refurb "plug n play" ECM they sent me was the wrong part. Of course the dealer installed it and it was useless. They tried to reprogram it twice. Of course that didn't work either.
Because the check engine light was off with only 1 monitor active (legal), I decided to see if I could slip it through inspection because it was now overdue. No problem. They slapped a new inspection sticker on it and off I went. I just pulled out of the garage into the parking lot and the check engine light popped on. LOL!
I ordered a new ECM (AC Delco) and they installed it, and programmed the thing. Done in under one hour. Because I had got it inspected, I could have ignored it and just put up with the check engine light on til the next inspection, but went ahead and had it installed anyway.
All said and done, they say the computer was absolutely the problem, and I had them recheck the purge valve before installing it. So we'll see. Hopefully this is the end of this story.