Air-fuel ratio control system

In an air-fuel ratio control system for an internal combustion engine having a carburetor including an intake passage, an electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied to said carburetor, an O.sub.2 sensor for detecting oxygen concentration of exhaust gases from the engine, a temperature sensor for detecting the engine temperature, an acceleration detecting sensor for being operated corresponding to negative pressure in said intake passage of the engine, and a closed loop control circuit responsive to outputs of all of the sensors for producing a control output signal for driving said electromagnetic valve for correcting the air-fuel ratio, the improvement comprising

• a switching circuit means provided in said control circuit for rendering said control circuit non-responsive to the output of said O.sub.2 sensor,
• gate means responsive to outputs of said temperature sensor and said acceleration detecting sensor for actuating said switching circuit comprising an AND gate connected to said temperature sensor and said acceleration detecting sensor, and
• said gate means being so arranged to actuate said switching circuit means in such a manner that air-fuel ratio correction control with the closed loop control circuit is carried out when engine temperature is higher than a predetermined temperature and stopped when engine temperature is lower than said predetermined temperature and said acceleration detecting sensor is operated.