Frequency Solenoid Valve "A"

Fig. 38 Operating Conditions For Frequency Solenoid Valves A and B:

After being controlled by the X-system to near stoichiometric air-fuel ratio, the mixture is more finely controlled based on the engine load.
The M-system consists of air control valve A and frequency solenoid valve A.
The diaphragm chamber of air control valve A receives the same carburetor vacuum as the EGR valve, and air is supplied to the intake manifold in proportion to the carburetor intake air volume. Frequency solenoid valve A gets signals from the oxygen sensor through the control unit and opens the valve when the air-fuel mixture is richer than stoichiometric.