Abstract: When feedback control of air/fuel ratio is not being performed in an engine and the engine is idling, the fuel supply amount is increased according to the engine coolant temperature. When feedback control of air/fuel ratio is not being performed and the engine is not idling, the fuel supply amount is decreased according to the engine coolant temperature. Due to this decrease correction, during the time period from when idling operation is terminated directly after starting the engine to when the feedback control of the air/fuel ratio is started, the air/fuel ratio is made lean at an early stage, and the oxygen concentration in the engine exhaust gas is increased, so that the conversion of HC by the catalyst is quickly started.

Abstract: An exhaust passage is connected to an intake passage of an engine through an exhaust recirculating valve. A target opening of the exhaust recirculation valve is first set according to a target exhaust recirculation rate depending on engine running conditions, the total intake air flow cross-sectional area of the engine, and a first correction value set according to the exhaust pressure. By applying this corrected value, the same EGR is always obtained on both low ground and high ground regardless of the engine running conditions. Preferably, the target opening is further corrected by a second correction value set based on the exhaust temperature.

Abstract: A fuel supply amount to a spark ignition engine is increased and an ignition timing of an air-fuel mixture is retarded during cold startup. At the same time, it is determined whether or not the air-fuel ratio of the air-fuel mixture is richer than a predetermined level, and retardation of the ignition timing is prohibited when it is richer than this predetermined level. In this way, retardation of ignition timing is prohibited when the air-fuel ratio is very rich immediately after startup. Combustion immediately after startup is therefore stable, and the discharge amount of HC is effectively reduced.