Idling rpm feedback control method having fail-safe function for

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. The supplementary air quantity control means comprises (1) a solenoid valve arranged across an air passage for controlling the supplementary air quantity through the above air passage, one end of which communicates with the intake passage of the engine at a location downstream of a throttle valve arranged therein and the other end with the atmosphere, respectively, or (2) a negative pressure-operated means for operating the aforesaid throttle valve in repsonse to the amount of negative pressure in the intake passage at a zone downstream of the throttle valve, and a negative pressure control means for controlling the amount of negative pressure in the intake passage, that acts upon the negative pressure-operated means.