Engine just started over revving. It was surging up and down. Diconnected the battery, eventually, and it ran fine for a while. Any ideas what is causing it?

 

I'd start by cleaning out your IACV. No CEL, right?

 

Yes, check engine light is on, honestly think it was on before this issue occurred. It is my son's car, and he is a couple hours away at college. I went up and replaced a radiator hose this weekend and had auto parts store pull codes. O2sensor on heated side and something on heater. I let car idle for 20 minutes or so while looking for obvious things like loose vacuum, but it did not act up for me. He is coming home this weekend, I will try cleaning the IACV with him and let you know. Thanks.

 

I agree with RedRyder. It sounds like the problem is your idle air control valve.