When the engine is running, the air intake valve is lifting up.
If the valve does not operate properly, check the air intake solenoid valve hoses for leak.
If there are no leaks, check the air intake solenoid valve.

Air Intake Solenoid Valve Unit TestAir Switching Valve (Service Code 64)
Air Switching Valve Removal/Installation
Refer to the Air Switching Valve Removal/Installation in
the Engine Top End chapter.
Air Switching Valve Inspection
Refer to the Air Switching Valve Unit Test in the Electrical
System chapter.
If the air switching valve [A] is normal, check ...
Subthrottle Sensor Resistance Inspection
Turn the ignition switch to OFF.
Disconnect the subthrottle sensor connector.
Connect a digital meter [A] to the subthrottle sensor connector
[B].
Measure the subthrottle sensor resistance.
Subthrottle Sensor Resistance
Connections: BL lead [D] ←→ BR/BK lead [C]
Standard: ...
Clutch Cover Installation
Using a cleaning fluid, clean off any oil or dirt that may
be on the silicone sealant coating area. Dry them with a
clean cloth.
Apply silicone sealant to the area [A] where the mating
surface of the crankcase touches the clutch cover gasket.
Sealant - Liquid Gasket, TB1211F: 92104-000 ...