Mixture Control System: Operation

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