over revving problem..

[wilken370Z]

Hello everyone, so I bought my 2009 370z about a year ago, only has about 23,000 miles on it. And I've had some major issues lately. Whenever I drive it, doesn't matter hot/cold, morning/night, I'll be sitting at a stop light, or just coasting in neutral, and it starts idling at almost 3,000rpms or higher.
I have actually sat at a red light and watched it climb from it's usual about 500 rpm, up to 4,500! My foot is not on the gas I have even gotten out of the car and it still revs like it's racing. I haven't been able to find anyone else who has had this issue before so maybe I really do have the Z ghost haunting me. Granted I have a warranty so it is going to the dealership for sure, but I just wondered if anyone else has had this issue before or if anyone has any educated idea as to what it could be?