Abstract: An apparatus for controlling the idling speed of an engine is disclosed. An idling speed control valve disposed in an idle passage communicates with the intake passage downstream and upstream of the throttle valve to control the amount of the airflow supplied to the idling engine. A neutral start switch outputs an instruction signal to an ECU based on a switching operation of a shift lever from its neutral range to a drive range. Based on the instruction signal, the ECU computes a duty factor to increase the airflow amount through the idle speed control valve to a predetermined amount. The increased airflow amount is subsequently attenuated to a predetermined magnitude with an attenuation factor based on a change rate of the engine speed.

Abstract: Disclosed herein is a variable venturi carburetor including at least one pressure controlling port provided at the lower peripheral portion of the suction piston and adapted to face to a mixing chamber defined directly downstream of the venturi portion. The pressure controlling port is located at such a position as to communicate with the suction chamber and an atmospheric pressure chamber during middle and high intake air flowing stages as the suction piston reciprocates transversely with respect to the venturi portion, and to communicate with the suction chamber and the mixing chamber during low intake air flowing stage.