Engine revs up when in park

I have a 2001 Saturn SC2, and occasionally when I put it in park after driving, it will rev up at a steady pace and just keep raising up the rpm, it does not stop unless I either put it back in drive (rpm drops way back down and shifts very hard) or, shut down the engine. If I go with the first method, shifting back into drive, right when I put it in park again it continues to do it and wont stop unless the engine is shut down, which feels terrible. It also will idle low and rough when its in park and not revving up as I said before. I have cleaned out the throttle body, cleaned up the IAC as much as possible, it has a new front oxygen sensor (because it went bad) and I even use injector cleaner every few times at the pump to ensure cleanliness since Saturns usually all seem to run rich. Anyways, these problems are driving me crazy and I’m stuck between a new IAC or a throttle position sensor. Am I wrong? please help so I dont waste money or cause damage!