If your Yamaha Moto4 80cc Badger speeds up while idling without touching the throttle, it could be caused by one of the following issues:
Throttle plate stuck?
throttle positioning sensor
Check throttle plate in throttle body throat - may be stuck open
Perhaps throttle plate is stuck - try to free with a screwdrive in the throttle body
A failing throttle position sensor will cause idling problems when the car is warm. The failing sensor can also cause the car to stall when idling.
Check the throttle position sensor
It could be that your car is idling to low, the throttle position sensor can be bad
Clean the throttle body or replace the idle air control valve
The bad idling may be due to a faulty Throttle Position Sensor (TPS). Have the computer scanned for trouble codes to confirm before replacing.
Throttle plate stuck in open position
It's the phillips screw where the throttle cable leads into the choke
if it's idling rough, I would suggest cleaning the throttle body with carburetor cleaner.