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A hot-wire air flow sensor which can directly measure the intake air mass flow has been developed, and a microprocessor based engine control system using the sensor has been designed. The sensing probe of the sensor is formed from a small wire-wound resistor, and installed in the bypass of the intake passage. The sensor requires a good signal processing method under pulsating flow conditions because of its quick response. New control technologies were examined for the prototype engine control system, using the sensor, as applied to a 4 cycle, 4 cylinder engine. The air-to-fuel ratio, ignition timing, and EGR rate are controlled to their optimum values by a microprocessor which processes signals of this sensor and of other sensors indicating the engine operating conditions. The results of engine performance tests show that the output power, fuel economy and exhaust emissions are improved significantly in comparison with other fuel management systems.