general problems of the 2000 Cadillac Deville

Driving into my drive way I noticed that my car pulled in very fast. Normally, I idle in my car into the drive way, this time it was much faster and the engine was very accelerated. I parked the vehicle and the engine was accelerated up to 1850rpm. I pressed the gas pedal to free up the throttle, it made is worst. The vehicle rpm increased up to 2835 rpm and stayed stuck at 2835 rpm. After 10 to 15 seconds the rpm slowly dropped down to 1500 rpm and stayed at these revolution. I had to turn off the vehicle. It's normal idle rpm are 675-700rpm. This is a safety hazard for some one that does not know what to do when driving at a busy highway or regular city streets.