Abstract: A warning system for an air-fuel ratio control system for a electronic controlled internal combustion engine, where a basic fuel injection amount is corrected by a feedback correction factor determined by a signal from an air-fuel ratio sensor arranged in an exhaust pipe. An amplitude of the feedback correction factor caused by an acceleration of the engine, where the exhaust from cylinders is not completely mixed, is detected, and a warning can be given when the amplitude of the feedback correction factor is larger than a predetermined value. A malfunction in the air-fuel ratio system occurring in one cylinder can be detected. In a double O.sub.2 sensor system, where a sub-feedback loop is provided for correcting the feedback correction factor in accordance with a signal from the second O.sub.

Abstract: An improved exhaust gas control valve of the type in which a vacuum actuated, valve-closure member controls the flow of exhaust gas into a gas chamber located between an inlet port and an outlet port, wherein the improvement comprises a corrosion-resistant metal liner covering the inside walls of the gas chamber, inlet port and outlet port that are exposed to the exhaust gas.