Variable Inertia Charge System (VICS) Check Valve (One-Way)
WARNING: This page is about a different car, the 2003 Mazda Protege5, 2003 Mazda Protege, 2003 Mazda MX-5 Miata, 2003 Mazda MPV, and 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
Remove VICS check valve (one-way). Blow air into port "A" and ensure air flows from port "B". See Fig 1. Blow air into port "B". Air should not flow from port "A". If airflow is not as specified, replace VICS check valve (one-way).