This isn’t a solution to the problem OP is having. Imagine the halo warthog, where players are jumping into and out of the vehicle at any given moment; You want it to set acceleration and steering back to 0 when the driver exits, but still otherwise have it behave like a vehicle, at the very least, while it coasts to a stop.
That said, If the vehicle needs a controller to receive any input, so be it, but it would have been nice if it threw out a warning somewhere so one wouldn’t spend a bunch of time trying to figure out why the seemingly obvious solutions aren’t working.