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 Intake Duct Assembly (Other than US, CA and CAL Models)
Install the seals [A] as shown in the figure.
Fit the projections [A] of the air intake valve to the hole [B]
of the air intake ducts.
Tighten:
Torque - Air Intake Duct Assembly Screws: 1.5 N·m (0.15
kgf·m, 13 in·lb)
Hang the shaft [A] to the air intake valve securely ...
Flap and Rear Fender Rear Removal
Remove:
Front and Rear Seat (see Front/Rear Seat Removal)
Seat Covers (see Seat Cover Removal)
Vehicle-down Sensor Connector [A]
Screws [B]
Clear the seat lock cable [C] from the seat lock unit [D].
Take off the seat lock unit and the bracket.
Remove:
Bolts [A] (Both Sides ...
Cam Wear Inspection
Remove the camshafts (see Camshaft Removal).
Measure the height [A] of each cam with a micrometer.
If the cams are worn down past the service limit, replace
the camshaft.
Cam Height
Standard:
Exhaust 35.043 35.157 mm
(1.3796 1.3841 in.)
Intake 38.243 38.357 mm
(1.5056 1.5101 in. ...