WHILE IN REVERSE, IDLING SLOWLY TO A STOP TO PICK UP A HOT WATER HEATER, THE VEHICLE SUDDENLY ACCELERATED INDEPENDENTLY. THE VEHICLE DID NOT RESPOND WHEN THE BRAKE PEDAL WAS DEPRESSED. AS A RESULT THE VEHICLE CRASHED INTO A PLUMBING SUPPLY WAREHOUSE, SENDING THE VEHICLE THROUGH AN OVERHEAD DOOR AND THROUGH EXPENSIVE HOT WATER HEATERS AND SPAS. THE VEHICLE CONTINUED INTO THE WAREHOUSE UNTIL IT HIT AN IMMOVABLE OBJECT AND STOPPED. THE THROTTLE CONTINUED TO HIGHLY REV THE ENGINE AND THE VEHICLE WAS SHIFTED INTO DRIVE TO GET OUT OF THE WAREHOUSE. THE VEHICLE CRASHED AT HIGH SPEED ON THE WAY OUT, AND ONTO THE STREET. BRAKES DID NOT STOP THE VEHICLE. THE VEHICLE WAS EVENTUALLY SHIFTED INTO NEUTRAL AND THE THROTTLE RESUMED NORMAL SPEED OPERATION. NEXT DAY, TOYOTA DEALER COULD NOT DIAGNOSE THE THROTTLE PROBLEM BECAUSE, BEING A 2004, IT DID NOT THROW COMPUTER FAILURE CODES. INDEPENDENT GARAGE DIAGNOSED THE PROBLEM AS A FAILED THROTTLE POSITION SENSOR. EARLIER IN THE SAME WEEK, THE THROTTLE STUCK OPEN WHEN BACKING UP AT LOW SPEED, BUT I DIDN'T THINK ANYTHING ABOUT IT OR THE SERIOUSNESS OF A FAILING THROTTLE. THE TRUCK IS NOW OPERATING AFTER REPAIRS.