Air-fuel ratio feedback control system for internal combustion engines, having function of correcting position of air/fuel ratio control valve actuator

In an air/fuel ratio feedback control system for performing feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine, which includes means for detecting the concentration of an exhaust gas ingredient emitted from the engine, fuel quantity adjusting means for producing the mixture being supplied to said engine, means operatively connecting said concentration detecting means with said fuel quantity adjusting means in a manner effecting feedback control operation to control the air/fuel ratio of said mixture to be a predetermined value, said connecting means comprising an electrical circuit, valve means for varying the air/fuel ratio of said mixture, and a pulse motor arranged to be controlled by said electrical circuit for driving said valve means, the combination comprising position detecting means for producing an output when said pulse motor is at a predetermined reference position which is set within a movable range of said pulse motor, a memory storing a value indicative of said predetermined reference position for said pulse motor, a first register responsive to an output signal of said concentration detecting means, indicative of the concentration of said exhaust gas ingredient, to make accessible a predetermined desired value for said pulse motor, a second register storing a value indicative of an actual position of said pulse motor, means for driving said pulse motor until said actual position value in said second register becomes equal to said predetermined desired value, and means responsive to said output of said position detecting means to cause shifting of said predetermined reference position value stored in said memory to said second register to replace the value stored in the latter by said predetermined reference position value.