We had a Cadillac that did that as well - it would rev up and get set to take off on its own - I had both feet on the brake peddle at an intersection when it first happened - turned out to be in the "computer" part of the brain of the car. Yes, turning off the ignition is great - - but remember that when you do, your power steering no longer works nor do your power brakes - so you need to take "strong physical command" until you can get it stopped.
Marysewfun