Abstract: A device is disclosed, which is intended for reducing the fuel consumption and the environmental pollution. An auxiliary power unit is provided, which is energized when a sensing mechanism signals to a signal-processing and control circuit that the engine is idling, for example, at a traffic light stop, or that a deceleration of the vehicle occurs. The fuel intake is cut off and a timing system provides to exclude the fuel feed to the engine for a certain selectable time. When such conditions are sensed, the auxiliary power unit (hydraulic or electric) provides to have the engine running without fuel use up. As normal traffic conditions are resumed, fuel is readmitted and the usual operation is started once again.