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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!

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If the reving drops back to normal when you shift in neutral, you should do that before shifting in drive since shifting from park to drive while reving up the engine causes high stress on the transmission.

I don't think it's the throttle sensor that is going bad since in drive the engine is not reving up.

You should go into an Autozone and ask them to plug an OBDII sensor into your car so you can have an error code, they should do this for free and we will have more info to help you with your problem.

  • When I am driving and I stop, I go to put the vehicle in park before I get out of it. When I shift from Drive to Park the engine revs itself and slowly climbs higher and higher and will not stop unless I power off the engine or put it in Drive or Reverse. It still will rev the same way if it is in Park or neutral. I have an OBDII scanner at home and have had no trouble codes since I replaced the front O2 sensor – Noah Clark Nov 12 '18 at 15:56
  • As I said in my previous response, don't ever put the car in drive/reverse while the engine is not at idle. As for your problem, it may be that you have a leaky or clogged PCV valve. It could also be a problem with the idle setting in your ECU, since it only happens when you're in park/neutral. – Samuel Perron Nov 12 '18 at 16:21
  • Oh okay, well I do like you said. I always wait for the engine to slow down before putting it into park. I replaced the faulty PCV valve when I got the car not long ago and its still doing great. I gave in and replaced the IAC to see if it would fix the problem, and after that it did it almost every time I put it into park for about the first 2 times I drove it, and now it hasn't done it since. – Noah Clark Dec 12 '18 at 18:36
  • IAC has to learn how you drive, a component could have went out in the IAC and didn't allow it to detect park, if park shorted out that might have been you problem, I myself would be tearing apart the old IAC and see what arched or malfunctioned. The idle is controlled by the IAC, if it cant keep the engine idling it will keep trying to rev the engine up to compensate – user38183 Dec 22 '18 at 8:56

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