A device for sensing the emissions from an idling engine and automatically adjusting the engine so as to minimize pollutants in the exhaust. The device measures the composition of gas emitted and the engine speed at idle and compares the measured values to predetermined values. When differences occur between the measured and predetermined values, an actuator is signaled which adjusts the position of an air-regulating screw and an idling screw in the carburetor until the measured values are acceptable.