Abstract: A method for controlling the air-fuel ratio in an internal combustion engine which includes the steps of changing the air-fuel ratio to a predetermined extent, detecting changes in the operating conditions of the engine by running the engine on the basis of the changed air-fuel ratio, and correcting the air-fuel ratio in the desirable direction for changing the air-fuel ratio on the basis of the detected desirable direction of change of the air-fuel ratio. The reading of the fuel correction coefficient K.sub.1 is carried out by using maps indicating the relationship between the number of fuel injections, the number of engine rotations, or the fuel injection period, and the fuel correction coefficient K.sub.1, respectively, for each ON and OFF mode of the bypass air control valve for controlling the air flow, by bypassing a throttle valve, and the fuel injection on the basis of the amount of fuel injection corrections read from the fuel correction coefficient K.sub.1.