Car Accelerates On Its Own problems of the 2008 Toyota Scion Xb

I recently experienced a "sudden acceleration incident". Our 2008 Scion Xb was driven over 122,000 miles without major malfunction until 3:30 pm on September 26 2014. Then, after stopping at our mailbox on the left side of the road, I proceeded 15 feet to our driveway entrance and made a left turn to position the car to pass through our gate, about 20 feet ahead. My speed was under 5 mph. I may or may not have touched the brake and/or accelerator pedal to adjust speed. Suddenly, the engine roared into wide-open-throttle and the car lurched forward. The car went through the gate, grazing the left gatepost, which shattered the left-front hubcap and sheared off the left mirror mount. The car then careened down our driveway while I attempted to steer and apply the brake. After about 2 seconds, during which the car traversed about 100 feet down the driveway, the engine abruptly slowed to normal and the brakes stopped the car. Damage included the sheared-off left mirror assembly, left-front hubcap, and minor denting of the left-front wheel well. The car engine has behaved normally since but has not been driven beyond our driveway. I experienced no impact or injury, aside from shock.