The guys at Advance said I needed to replace the O2 sensor on bank 1, but several websites said a dirty MAF was the most likely culprit. The car runs fine. So I cleaned the MAF and reset the codes, but it recurred after a few minutes of idleing.

What would you recommend as my next step? Replace the MAF, replace the O2 sensor, or what? Websites seem to suggest that this could also be a vacume issue.

BTW, I don't know if it is related, but I also have an intermittent AC problem where the system won't come on at all. The panel lights up and I can hear the compressor come on, but the fan doesn't blow. Then it will start running randomly as I am driving. Very strange.

I don't believe you need to change your MAF, you would have other issues if the MAF was the problem. A vacuum leak is a likely cause of this code. Here is a write up I did a while back on this code. https://www.gmforum.com/obd-ii-trouble-shooting-153/p0171-284036/ This code can come up when you have unmetered air entering the system between the MAF and the O2 sensor. So even a exhaust leak can cause this code.

The factory FSM'* suggest the maf as a potential cause of the issue. However in finding and diagnosing this code many times, I've never found the maf to be the problem.

Vacuum leaks are the most common cause
Next up would be bad ground from corrosion in the cables. If the cable has enough corrosion in it, it'll throw off the various sensors and cause the car to run lean. Had this one happen to me personally.

Thanks guys. I guess I have some hunting to do.