Check The Mass Air Flow Sensor Unit

Remove the mass air flow and intake air temperature sensor. Refer to Fuel Injection (Fuel Systems) (H4DO)>Mass Air Flow and Intake Air Temperature Sensor>REMOVAL .
NOTE: Do not disconnect the connector.
Turn the ignition switch to ON. (Engine OFF)
Using the Subaru Select Monitor, read the intake air amount. Refer to ENGINE (DIAGNOSTICS) (H4DO)>DATA MONITOR .
Check that the intake air amount changes when air is blown to the mass air flow sensor unit in the arrow direction.
CAUTION: Be careful that no dust enter inside the unit when air is blown.

Courtesy of SUBARU OF AMERICA, INC.
After inspection, install the related parts in the reverse order of removal.