VEHICLE WAS STUCK IN FULL THROTTLE WHILE DRIVING ON THE HIGHWAY. WHEN THIS OCCURRED THE BRAKE PEDAL WAS DEPRESSED BUT FAILED TO STOP OR SLOW THE VEHICLE DOWN. AS A RESULT, CONSUMER HIT THREE MOTORISTS BUT VEHICLE CONTINUED TO ACCELERATE. THE EMERGENCY BRAKE WAS ENGAGED AND VEHICLE WAS PUT IN PARK GEAR TO STOP. *AK THE PROBLEM WAS DUE TO A PEBBLE ENTERING THE AIR INTAKE VALVE. *LA