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 TestEvaporative Emission Control System (California
model only)
This system routes fuel vapors from
the fuel system into the running engine
or stores the vapors in a canister when
the engine is stopped. Although no adjustments
are required, a thorough visual
inspection must be made at the intervals
specified by the Periodic Maintenance
Chart.
Inspection
...
KIBS Hydraulic Unit Inspection
Remove the KIBS hydraulic unit (see KIBS Hydraulic Unit
Removal).
Visually inspect the connector terminals [A].
Replace the KIBS hydraulic unit or main harness if either
of the terminals are cracked, bent, or otherwise damaged.
If the KIBS hydraulic unit connector is clogged with mud
or ...
Clutch Plate Warp Inspection
Place each friction plate or steel plate on a surface plate
and measure the gap between the surface plate [A] and
each friction plate or steel plate [B] with a thickness gauge
[C]. The gap is the amount of friction or steel plate warp.
If any plate is warped over the service limit, repla ...