Abstract: An engine control system is disclosed which includes engine idle speed control apparatus which implements a closed loop idle speed control by varying the amount of air provided to the engine by an air bypass valve. The control system develops an engine torque polarity signal related to the difference between actual current manifold air pressure and the average of the manifold air pressure which exists during engine idle. The torque polarity signal is utilized to implement engine deceleration control by selectively providing additional air and/or reduced fuel to the engine to implement engine fuel mixture enleanment during deceleration conditions. The engine idle speed control apparatus calculates an error signal related to the difference between actual engine speed and a calculated desired engine idle speed.