Abstract: An evaporative fuel-purging control system for an internal combustion engine, which controls purging of a mixture of evaporative fuel from a fuel tank and air comprises a purge control valve arranged across a purging passage for controlling the flow rate of evaporative fuel from the fuel tank to an intake passage. The flow rate of evaporative fuel is detected and compared with a desired flow rate commensurate with an operating condition of the engine. The valve opening of the purge control valve is controlled in response to results of the comparison. The change rate of the valve opening is varied according to the concentration of evaporative fuel in the mixture. Specifically, the change rate is decreased as the evaporative fuel concentration is higher.

Abstract: Deterioration of an exhaust gas concentration sensor for an internal combustion engine is detected by integrating a difference between an output from the exhaust gas concentration sensor and a predetermined reference value which is outside a range of the output which can be assumed during normal operation of the exhaust gas concentration sensor, comparing a thus obtained integral value with a predetermined deterioration-determining value, and determining from the result of the comparision whether the exhaust gas concentration sensor is deteriorated.