Well my one-year old 2017 Volt just did that on the Highway at 50 km/hr and it kept accelerating after I took my foot off the pedal. I braked, the car slowed down; I took my foot off the brake without touching the accelerator pedal and it started to accelerate again. Went through that cycle twice and finally I reached down and pulled the accelerator pedal up and that cured it. Scary. Just to check, I repeated the exercise and it is repeatable. Car was driving in default Normal mode with gas engine running because of the temperature (-13C); car had driven about 2km after fully charging the battery and sitting in the garage overnight. In the good old days, I would have concluded that the throttle linkage was stuck/frozen, but that isn't supposed to happen anymore. As I recall, Toyota had an similar "issue" a few years ago. Oh yes, there is no problem with the accelerator pedal interacting with the carpet. I checked. Moral: don't floor your Volt.