Car Accelerates On Its Own problems of the 2002 Toyota Sienna

I was pulling forward from a red light, slowly accelerating. Someone cut me off, I swerved, and then accelerated into traffic. The car started accelerating on its own, from about 35 mph (where I pulled my foot off the accelerator pad to "hold" the speed but not continue accelerating) up to 55 mph--this happened very quickly, in a smattering of seconds. I remembered reading that you should just slam on the brake and hold it down hard, which I did. This did stop further acceleration, but it did not immediately slow the car. I was able to slow the car in about 10 seconds, though deceleration was very slow. When I finally returned to 35 mph, I did not attempt to accelerate again for about two miles. I stopped at another traffic light, and when I started forward from the light, I did not depress the accelerator pad with my typical force, accelerating at about half the speed I normally would, as I did not want to be taken by surprise by the unexpected sudden acceleration again. The problem did not further repeat itself this evening, but it was quite scary when it happened. I know it was not the floor mat under the pedal, as the floor mat has been cut away from the pedal area and was pulled very far back into the driver's seat area.

Toyota Sienna van appeared to have sudden acceleration problem when stopped at stop sign. Engine revved up as accelerator was about to be applied, so I had to apply brakes as car was making sudden movements. Quickly put car into neutral position.