Charge Relief 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 charge relief valve. Connect vacuum pump to port "A" of valve. See Figure . Apply 8 in. Hg vacuum to port "A", and blow air into port "B". Replace charge relief valve if air does not flow from port "B" to port "C".