IDLE SPEED CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE

An idle speed control system for an automotive internal combustion engine having an intake air passageway through which intake air flow to be inducted into engine cylinders. The idle speed control system is comprised of an auxiliary air control valve operatively disposed in an auxiliary air passage which is connected with the intake air passageway in a manner to bypass a throttle valve. The amount of air flowing through the auxiliary air passage is regulated by controlling the opening degree of the auxiliary air control valve under an idle operating condition in order to control idle speed. The control of the auxiliary air control valve opening degree is accomplished in accordance with a difference between model and actual torques of a power output shaft of the engine. The model torque is produced in time series in accordance with a target idle speed by using a model.