Importance

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Abstract

A vacuum-operated actuator controls opening and closing of a throttle valve in an intake passage of an internal combustion engine in response to pressure in a vacuum chamber thereof. A change-over control valve supplies the vacuum chamber, selectively, with first and second control pressures for opening and closing the throttle valve, respectively. An electronic control unit controls the engine idling rotational speed by generating an on-off control pulse signal having a period corresponding to the engine rotational speed, and supplying the change-over control valve with the on-off control pulse signal to cause same to supply the vacuum chamber with the first or second control pressure. The electronic control unit determines the engine rotational speed and a rate of decrease in the engine rotational speed, and halts the idling speed control for a predetermined period of time when the determined engine rotational speed falls within a predetermined range and at the same time the determined rate of decrease falls within a predetermined range. A valve opening-correcting device corrects the throttle valve opening to a larger opening in response to at least one predetermined external load applied on the engine. The electronic control unit actuates the valve opening-correcting device to increase the throttle valve opening which is determined by the change-over control valve in response to the on-off control pulse signal.

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First Claim