When idling, the rpms fluctuate up and down so bad it stalls. you can 'two foot' it and get going - sets codes that are for too rich AND too lean. I replaced the catalytic converter because the old one was bad. If I unplug the MAF, it idles OK, a little high, sets MAF code of course. Can't help but think this will lead to other problems. I would prefer no code AND a stable idle. A fellow engineer from GM, the engine guy on our team was helping me. He said to drive up to 35 mph and coast down so the ecm could relearn. I have done this and it only helps temporarily.

erratic idle and erratic gps grams per second on scan tool usually indicate bad MAF.Try cleaning MAF first.A labscope or scan tool needed at least a scan tool to look to see what MAF is telling PCM.