Hi, next time, take off the air filter and starve it of air, it will soon stop then. Did it have a lot of fuel left in the tank, was the carb closed when it ran away? It could be a leaking bearing or an air leak from somewhere else,, if an engine pulls in air then it will idle erratic or won’t start, leaking front bearing by flywheel is quite common, or carb not sealing correctly against body of car, what engine is it, what fuel are you using? Nitro is fiddly but fun when they run right.
Mart