1990 Mercury Grand Marquis

I EMBARKED ON A ROUTINE TRIP TO DINNER IN MY MOTHER'S 1990 MERCURY MARQUIS. I STARTED THE ENGINE WHICH IDLED NORMALLY, AS USUAL. WITH MY FOOT ON THE BRAKE, I ENGAGED THE SHIFT LEVER INTO THE R POSITION WHICH RESULTED IN IMMEDIATE ACCELLERATION IN A REVERSE DIRECTION. I SWERVED THE CAR TO THE LEFT TO AVOID CHILDREN ACROSS THE STREET AND RAMMED A VEHICLE PARKED ON THE STREET. THE VEHICLE STOPPED ON IMPACT WITH THE OTHER VEHICLE AND RETURNED TO NORMAL IDLE SPEED. I PLACE THE CAR IN D AND RETURNED IT TO THE DRIVEWAY WHERE IT REMAINED UNTIL WE COULD DELIVER IT TO OUR FAMILY MECHANIC. HE PLACED THE ENGINE ON HIS ANALYZER - DID OTHER INSPECTIONS OF BRAKES, CRUISE CONTROL AND OTHER THROTTLE RELATED SYSTEMS AND FOUND NOTHING.