Mixture Control System: Operation

When sudden deceleration occurs, high manifold vacuum acts on chamber B of mixture control valve. The valve opens and fresh air is drawn in through MC valve filter to intake manifold where it helps maintain a balanced air/fuel mixture. After a few seconds, vacuum in chamber A will balance vacuum in chamber B. The MC valve closes and no additional air is brought into intake manifold. Deceleration fuel control is then maintained by throttle positioner or deceleration fuel cut system.