Fuel Vapor Valve
WARNING: This page is about a different car, the 1995 Mazda RX-7. However, it is still accessible from the selected car via links, so may be relevant.
Remove fuel vapor valve. Blow air into hose connection port on valve. When held in normal upright position, air should flow through valve. Turn valve upside down. Air should not flow with valve upside down. Replace valve as necessary.