Abstract: An engine intake system including an intake passage opening to the combustion chamber through an intake port having an intake valve. A control valve is provided in the intake valve for cyclically opening the intake passage. Upstream the control valve, the intake passage is provided with a tank which functions to reverse the negative pressure propagated from the control valve into a positive pressure which is then transmitted to the combustion chamber to increase the intake charge. A timing control mechanism is provided for retarding the opening timing of the control valve in a low speed, high load engine operation.

Abstract: An internal combustion engine has an intake system provided with a valve for controlling the intake air flow in an idling operation. There is provided a control system including an engine speed detector and a control circuit which compares the engine speed signal from the engine speed detector with a reference value corresponding to a desired idling speed to produce a feedback signal for adjusting the valve. There is also provided an external load detector for producing a modifying signal when an external load is applied to the engine in the idling operation. The control system functions to interrupt the feedback control under the feedback signal for a predetermined time when the external load is applied or removed so as to stabilize the engine speed in a transient period.