Engine revs to about 2500 RPM when shifted to park and stalls intermittently

Hey guys, new to forum thanks upfront for any help. I got a 2009 Aveo LT with a automatic transmission. I bought it at auction in the summer of '13 with 165k miles. I immediately changed the timing chain and water pump. About a year later it started stalling and I replaced the ignition coil, problem solved. About two weeks ago I noticed after driving for a little while and then placing the shifter in Park it would rev up to about 2500k then come back down. It did that for about a week and then started idling rough and would sometimes stall stopped at traffic lights. The MIL was on so I checked the codes and they were all related to the downstream O2 sensor. I replaced it a couple days ago but that did not alleviate the problem. I cleaned the MAF sensor and that didnt help either. I am curious if anyone has had a similar issue or any ideas what it could be. The parts are expensive and I am trying to avoid just buying parts that might not be the problem. The O2 sensor was already $140 and a new MAF sensor is another $120 and that might not fix anything. There is no loud hissing that would suggest a vacuum leak and the car has no problem doing 80mph on the interstate so I dont think there is anything wrong with catalytic converter. There have been no new check engine lights or codes to check but the car is still doing the same revving up in park, idling rough, and sometimes stalling at traffic lights. Any ideas?

I would guess it would be the cold start/temp sensor. Codes wouldn't set until in closed loop, and that is a "rough" start up circuit = no codes.