general problems of the 2006 Jaguar XJ

While stopped in the road waiting for another car. With foot on brake, the car suddenly goes full throttle. Driver has both feet applied on the brake and the car still moves forward burning rubber, and then after a few seconds it goes back to idle. The car does this once or twice a year, the last time doing damage to a car in front of it. This is the fifth time this has happened. The car is idling normally with the right foot on the brake and it will just go full throttle all by itself. It has happened enough that we know we do not have both the brake and the gas pedal depressed. From doing online research I believe Jaguar and Toyota / Lexus used the same system for controlling acceleration. I replaced the throttle body after the fender bender, it evidently did not help.