A new air-fuel ratio control algorithm and its effect on automotive engine operation is described. The system consists of a wide range air-fuel ratio sensor and a single point injector with an ultrasonic fuel atomizer. The air-fuel ratio control adopts PID control and it has built-in learning control. A 16 bit microcomputer is used for the latter.The results of three studies are given. The first deals with adaptive PID gain control for various conditions. The second is the new learning control which uses an integration terra. The third is individual cylinder air-fuel ratio control.