UKHeliBob:
No wonder the motor continues to run.
If you don't want moveForward() to be called each time through loop() then create a boolean variable, perhaps named engineCanRun, and make the call to moveForward() dependant on it being true. When you want to prevent the vehicle moving set the boolean to false and the function will not be called
I still do not know how to make the call to moveForward() dependant on it being true. 