The basic structure of a new engine control system for highly accurate air-fuel ratio control is introduced. Improved engine power and decreased fuel consumption are required for today's engines. Better air-fuel ratio control must be attained to set the air-fuel ratio to that of the maximum power and minimum fuel consumption.In order to enhance the accuracy of the air-fuel ratio control, the air flow meter, air-fuel ratio sensor, and fuel supply device are improved in the new system. Accuracy is lost in conventional system owing to the sensors' deterioration over long-term use. So prevention of air flow meter deterioration and compensation of air-fuel ratio sensor deterioration are taken into consideration. Fuel atomization of the fuel supply device is improved in order to reduce the air-fuel ratio fluctuation in the transient operating state.High power and decreased fuel consumption over long-term use are made possible with the new system.