Rob1224

so I was at school today, just came back from the store down the road and the engine (2001 i30) turned over and ran fine heading there and back, however, after waiting in the parking lot a while for my friend I turned the car back on and it was "ghost" revving to 2000Rpm for lack of a better term. The CEL IS on but we're pretty sure its an 02 sensor, would this have anything to do with the revving? I turned the car on and off and on the second time it didnt rev anymore.