System for controlling idling speed in internal combustion engine for vehicle with automatic transmission

DETAILED DESCRIPTION An object of the present invention is to provide an engine idling speed control system capable of decreasing the shock generated by manual operation of the automatic transmission device to attain a shift down operation for engine braking without complicating the construction of the device.
According to the present invention, a system is obtained for controlling engine idling speed for an internal combustion engine for a vehicle provided with an automatic transmission device, the engine being provided with an intake line and a throttle valve arranged therein, and the system comprising: a by-pass passageway connected to the intake line so as to by-pass the throttle valve; a valve arranged in the by-pass passageway for controlling the amount of the air passing therethrough; means for calculating the degree of opening of the valve corresponding to a present engine speed during a substantially fully closed condition of the throttle valve; means for producing a signal directed to the valve for operating the same so that the actual opening of the valve corresponds to the opening calculated by the calculating means; means for detecting a shift down operation of the automatic transmission device for attaining an engine braking effect; and, means for modifying the calculated degree of opening of the valve so that the amount of air allowed to pass therethrough is increased during the shift down operation, thereby causing the engine output torque to be increased.