THE VEHICLE ENGAGED IN INVOLUNTARY ACCELERATION (IN REVERSE) FROM STATIONARY POSITION RIGHT AFTER SHIFTING GEARS FROM PARKING 'P' TO REVERSE 'R' AND DISENGAGING THE PARKING BRAKE. THE BRAKES WERE BEING APPLIED DURING THIS GEAR CHANGE. THE CAR STARTED MOVING IN REVERSE AS SOON AS THE DRIVER LET OFF THE BRAKES. THE DRIVER THEN REAPPLIED THE BRAKES BUT THE VEHICLE ACCELERATED INSTEAD OF BREAKING. MORE PRESSURE WAS APPLIED TO THE BRAKES BUT THAT INCREASED THE SPEED INSTEAD OF REDUCING IT. THE VEHICLE ACCELERATED FROM 0 MPH TO APPROXIMATELY 50 MPH AND TRAVELED ABOUT 100 FEET IN REVERSE. THE DRIVER WAS MANEUVERING THE VEHICLE WITH THE STEERING WHEEL WHILE SIMULTANEOUSLY APPLYING PRESSURE TO THE BREAKS. THE DRIVER MANAGED TO STEER THE VEHICLE UP A SMALL GRASSY HILL OF ABOUT 15 DEGREES IN SLOPE UNTIL THE VEHICLE HIT A RESIDENTIAL CONCRETE WALL WITH THE BACK OF THE VEHICLE. AT THE MOMENT OF IMPACT, THE VEHICLE BOUNCED BACK AND THE ACCELERATION DISAPPEARED WITH THE ENGINE STILL ON. THE VEHICLE THEN SLOWLY ROLLED DOWN THE HILL UNTIL IT HIT A PARKED CAR. AT THAT MOMENT, THE CAR STOPPED AND REMAINED STATIONARY. THE ENGINE WAS THEN TURNED OFF. THE IMPACT CAUSED DAMAGE TO THE BACK OF THE VEHICLE AND TO THE RESIDENTIAL CONCRETE WALL. THE DRIVER'S SEAT WAS ALSO DAMAGED. IT BECAME LOOSE WITH THE IMPACT AND WAS EJECTED BACKWARDS TOWARDS THE BACK SEAT WITH THE DRIVER STILL ON IT. THERE WERE NO PHYSICAL INJURIES TO THE OCCUPANTS OTHER THAN WHIPLASH. A FIRMWARE DEFECT OF THE ELECTRONIC THROTTLE SY