Throttle is not springing back into the correct position
Sometimes accidental physical impact to the throttle could cause it to stop working, either from dropping the scooter or other impact. The easiest thing to do in this case is to replace the throttle. You can order a replacement piece here and follow the instructions below to install the new piece.
To remove the throttle, there is a single screw that first needs to be removed (3mm hex):
***The Levy Plus throttle is not as simple to replace. If you have a Levy Plus Scooter you may want to consider replacing the entire top unit.
Throttle is not engaging the motor
The throttle will not work if the hand brake is engaged. If the hand brake is broken or the brake line is rusted the brake may stay engaged even when not being used. A way to tell if this is the issue with your scooter is to check to see if the rear tale light is flashing while the brake is not being held. This light should only flash while the brake is engaged.
Throttle continues to engage the motor after I release it
If releasing the throttle does not disengage the motor the first thing to do is check to see if Cruise Control is enabled. Cruise control is a P1 setting and can be turned on and off through display menu. If Cruise control is on then the scooter will beep as soon as it engages and then continue to beep if you hold down the throttle. When you release the throttle the scooter will maintain its current speed. You can see how to turn this function on and off here.
If cruise control is not on but your scooter is still engaging the motor after the throttle is released, you likely have to replace the throttle.