Method and apparatus for regulating a combustible mixture

A fuel metering control loop which includes an exhaust gas sensor and an integrating controller. In order to operate the system at an air number which may differ from the most stable operating point of the oxygen sensor, the output signal from the controller is deliberately changed so as to override the command signals from the oxygen sensor. In particular, the output signal undergoes a step-change toward a higher or lower value at the times of reversal of sensor potential. Thus, the average value of the air number which the controller effectively maintains is different from the nominal value which would be obtained with direct sensor control. In another embodiment, the ongoing integration process is continued for some time beyond the sensor signal reversal.