Recently my 2006 Crossfire Convertible has started having an engine idling problem. The car starts fine, and everything is alright at startup. Once I start driving, the engine does not go back to idle correctly. Even when shifting, the engine will continue at about 1500 RPM while shifting. When I stop the car, it idles between about 1200 and 1600 RPM, for a while, then slowly drops down to its normal 600 to 800 RPM idle. The idle is high enough that in some gears I don't even need my foot on the accelerator for the car to continue going. Eventually, though, the car will drop the RPM to normal. The car drives fine except for this problem. Is this a known problem? Any suggestions?