The problem could be in the throttle or speed controller.
throttle cable from the speed controller and see what happens.
If the motor still runs at full throttle after disconnecting the throttle then the problem is in the speed controller and it will need to be replaced. If the motor stops running at full speed when the throttle is disconnected from the speed controller then the problem is in the throttle and it will need to be replaced.
When I turn the power switch on my scooter runs at full throttle all the time. until I turn the power switch off. What is the problem?