My wife was driving my 6.5td last night. She went to accelerate the engine kept accelerating. She braked against engine managed to stop with the engine running flat out. It stopped when she turned ignition and off. Weather was hot. Has been threatening to do the same to me in the winter wet. When I got there 2 hours later started and ran fine. No stalling issues. Anything come immediately to mind? Has anyone had this experience before?