I once had a diesel engine runaway (google it, the engine ran on its own oil at some insane rpm). I put it in neutral until the engine seized. Scary stuff
I believe petrol engines can do this too, and I didn’t mention it for petrol engines because the performance of the engine in that state won’t be anything like what it’s capable of, the rpm will go high but if you put any load on it the engine won’t be outputting a lot of torque or power. If this happens in a manual just push the brakes really hard while the car is in gear and clutch released, it will stop the engine. If it’s auto I guess you’re buying a new engine lol, but it’s not like the car is going to run out of control if you just stay calm
The correct course of action is stuffing up the air intake to suffocate the combustion, if this is still a viable option. Otherwise, depart from the vehicle and be ready to call the fire department.
I should have done that, hoping to stall the engine. I panicked and really didn’t know what to do. The noise and MASSIVE cloud of black smoke pouring out the back were terrifying. Not a great first drive after an engine swap.