of the input operating parameters application_number US 47498283 A description it is to be noted the present invention can be adapted for use in any one of various engine control systems whose operating parameters include air fuel mixture ignition timing recirculated exhaust gas and engine speed in a typical example the ratio of air fuel mixture is used in the present invention as a representative of such parameters referring now to fig1 the intake manifold pressure pm and the throttle opening u03b8 of an internal combustion engine in which the invention is adapted are illustrated graphically as a function of engine load with the engine speed n being kept constant it is seen that as a function of engine load intake manifold pressure decreases substantially exponentially while throttle opening increases but the rate of its increase also follows a substantially exponential curve according to the present invention the intake manifold pressure is used as a predominant factor for air fuel ratio control when the engine is operating under less loaded conditions and the throttle opening becomes the predominant factor instead of manifold pressure during the time the engine is under loaded conditions by doing so it is possible to compensate for variations in air fuel ratio that arise from variations in loading condition from idle to full loads since the rate of engine load variation is significant compared with those of other engine operating parameters precision control of air fuel ratio is made possible fig2 is a schematic illustration of a hardware structure of the air fuel mixture control system of the invention the system comprises a plurality of engine parameter sensors including engine.