By-Pass Air Control (BAC) Valve (MILLENIA)

On Millenia 2.3L, BAC valve is located on rear of front cylinder head. See Fig 1 . On Millenia 2.5L, BAC valve is located underneath throttle body. See Fig 2 .
On all models, ensure engine is cold. Start engine and let it idle. Idle speed should gradually decrease as engine reaches normal operating temperature. If idle speed does not decrease, check coolant hose to BAC valve. Repair as necessary. If coolant hose is okay, replace BAC valve.

Fig 1: Identifying BAC Valve (Millenia 2.3L)

Courtesy of MAZDA MOTORS CORP.

Fig 2: Identifying BAC Valve (Millenia 2.5L)

Courtesy of MAZDA MOTORS CORP.