CONSUMER PUT ON SEATBELT, STARTED THE CAR PUT IN REVERSE, AND CAR JERKED AND TOOK OFF BACKWARDS VERY FAST. WENT ACROSS TO YARDS, AND STILL RMP'S WERE REVVING VERY HIGH. VEHICLE CRASHED INTO A TREE ON DRIVERS SIDE. CAR HAD TO BE TOWED. MECHANIC SAID THAT THROTTLE WAS NOT STUCK. ALSO, BRAKES WOULD NOT STOP CAR, CONSUMER FELT THAT THROTTLE LEAKAGE AND CONTROL AND SUDDEN ACCELARATION PLAYED A BIG PART IN THIS INCIDENT. *AK