1999 Chevy Corvette high idle speed

Here is my problem. If I go from a standing position with the car in drive and the a/c on I release my foot from the brake with no foot on the accelerator and the car will accelerate on it's own up to about 28 miles per hour and the tach will read 1000 rpm's if I do nothing except put the shiffter into neutral the tach will shoot to about 1800 rpm's and still no foot on the accelerator if you do nothing and give the car about 10 seconds the engine will work it's way back to the 600 rpm idle speed from where you started. With this condition stopping becomes very jerky as the transmission down shifts under power with the brake on.
Your suggestions please.