Abstract: An idling rpm feedback control method for controlling control means that controls the quantity of supplementary air being supplied to an internal combustion engine in a feedback manner, in response to the difference between actual engine rpm and desired idling rpm at engine idling, when all predetermined engine operating parameters at least including the throttle valve opening show values satisfying a predetermined condition. When the throttle valve opening detecting means malfunctions, control is effected by maximizing the quantity of supplementary air to the engine by operating the above supplementary air quantity control means to its operating limit.

Abstract: An idling rpm control method for feedback control of a control valve for controlling the quantity of supplementary air being supplied to the engine in response to a difference between actual engine idling rpm and desired idling rpm. At the start of the engine, the control valve is continuously opened for a predetermined period of time from the time the engine rpm has increased above a predetermined value lower than the desired idling rpm, thereby maintaining the engine rpm at a value higher than the above desired idling rpm. The above predetermined period of time may desirably be set to a value as a function of engine temperature, preferably detected immediately after the engine rpm has exceeded the above predetermined value of engine rpm.

Abstract: A system adapted to control a control valve for controlling the quantity of supplementary air being supplied to an internal combustion engine, in a feedback manner responsive to a difference between actual engine rpm and desired engine rpm at engine idle. The above control valve is opened in synchronism with a signal indicative of a predetermined rotational position of the engine. The system is also adapted to detect a total quantity of suction air including the supplementary air being supplied to the engine, in synchronism with the above predetermined rotational position signal, to supply a quantity of fuel corresponding to the detected total suction air quantity.

Abstract: An exhaust gas recirculation control system which is adapted to control the valve opening of the exhaust gas recirculation valve so as to minimize the difference between a detected value of the valve opening of the above value and a command value determined as a function of operating conditions of the engine. The valve opening is corrected at a higher speed when the above difference has a larger absolute value, and at a lower speed when the difference has a smaller absolute value, to ensure prompt and accurate control of the exhaust gas recirculation quantity.