Cruise Control problems of the 2000 Mercedes Benz 320

The event involved my 2000 e320 sedan. I had driven to albuquerque and used my cruise control as usual - it was still on but not engaged. I entered kirtland afb, where I stopped at the guard shack to present my id and then started down wyoming street at 25 mph. Suddenly, the accelerator was drawn down to the floor and the car accelerated like a rocket! I grabbed the wheel with both hand and stood on the brake pedal with both feet, almost stopping before I overtook and hit a pickup truck that had been three blocks ahead of me. No injuries. About $5000 damage to my car from engulfing the huge towbar on the truck (grill, hood, radiator, power steering control, etc. - actually no major damage). Mercedes service people stated that they could find nothing wrong with the car to explain the spontaneous acceleration.