AIR/FUEL RATIO CONTROL SYSTEM FOR ENGINE

A learning control system for controlling an air fuel ratio an engine employs a slowly updated second learning control variable in addition to a normally updated first learning control variable in order to utilize the learning function sufficiently even when a deviation of the air fuel ratio exceeds the learning range of the first variable. The control system according to an illustrated embodiment of the invention identifies a current engine operating area among a plurality of such areas, in accordance with a sensed engine operating condition, obtains a value of the first learning variable corresponding to the identified operating area, and a value of the second learning variable, determines a learning quantity which is a sum of the first and second learning variables by using the obtained values, and uses this learning quantity for determining a desired fuel supply quantity. The second learning variable is updated slowly whereas the first learning variable is updated in a sensitive and speedy manner.