Abstract: An air-fuel ratio control system for an internal combustion engine has an exhaust gas component concentration sensor having a sensor element and arranged in the exhaust system of the engine, for detecting concentration of a predetermined component present in exhaust gases emitted from the engine. An ECU controls the air-fuel ratio of an air-fuel mixture supplied to the engine, based on results of comparison between an output value from the sensor and a predetermined reference value, and detects deterioration of the exhaust gas component concentration sensor, based on the output value from the sensor. Engine operating condition sensors detect operating conditions of the engine. It is determined whether or not the engine is in a predetermined engine operating condition in which the sensor element temperature of the exhaust gas component concentration sensor lowers, based on outputs from the engine operating condition sensors.

Abstract: An air-fuel ratio feedback control method for an internal combustion engine in which when the engine is operating in a feedback control region, the concentration of an ingredient in exhaust gases from the engine is detected by an exhaust gas ingredient concentration sensor arranged in the exhaust system of the engine and compared with a reference value, and the air-fuel ratio of an air-fuel mixture to be supplied to the engine is controlled to a desired value in a feedback manner responsive to the result of the comparison. Atmospheric pressure is detected, and the reference value is set to a value depending on the detected value of atmospheric pressure. The reference value is set to a higher value as the detected value of atmospheric pressure is lower. The reference value is set to a lower value when the engine is operating in an idling region than when the engine is operating in a region other than the idling region.

Abstract: An air-fuel ratio feedback control method for an internal combustion engine, in which when the engine is operating in a feedback control region, the air-fuel ratio of an air-fuel mixture being supplied to the engine is controlled by the use of a correction coefficient varying in response to the output of an exhaust gas ingredient concentration sensor arranged in the exhaust system of the engine. When the engine has shifted to a predetermined high load region within the feedback control region, in which the rate of change in values of an engine operating parameter is larger than a predetermined value, the air-fuel ratio feedback control is effected by the use of a first average value of the correction coefficient, calculated when the engine is in the predetermined high load region.

Abstract: A method of controlling the air-fuel ratio of a mixture being supplied to an internal combustion engine, in a feedback manner responsive to output from an O.sub.2 sensor arranged in the engine exhaust system for sensing the concentration of a component in exhaust gases from the engine to produce as the output a normally fluctuating output signal indicative of the concentration. The air-fuel ratio is controlled to a desired value by means of at least one of proportional control applying a first correction value to correct the air-fuel ratio when the output signal changes from a rich side to a lean side or vice versa with respect to a predetermined reference value, and integral control applying a second correction value to correct the air-fuel ratio whenever a predetermined period of time elapses so long as the output signal remains on the lean side or on the rich side with respect to the predetermined reference value.

Abstract: A fuel supply control method for an internal combustion engine in a cold state. A basic value of fuel supply quantity is corrected to an increased value by the use of a correction variable set based upon engine temperature and engine load. Intake air temperature is detected, and the correction variable is corrected by the detected intake air temperature. Preferably, the correction variable is corrected to a larger value as the detected intake air temperature is lower.