My 2004 Grand Prix has recently been reving up when I turn it on. This did it about 8mos ago, took it into the shop and they couldn't find anything wrong with it, they thought it could be some sensors so they replaced them. It seemed to have fix the problem until this week and it's doing it again. If I turn it off and back on sometimes that fixes it and it idles back to normal, other times I have to drive, turn it off and then back on and it will idle fine. It doesn't rev up when I'm driving, only occasionally when I start it. Any ideas what could be causing this? I don't want to take it in since this shop didn't know what could be causing it and to replace those sensors was expensive? Any thoughts would be appreciated before I bring it in. Thank you, Maxie.
