Abstract: The present invention relates to a disconnectable electromagnetic eccentric actuator for controlling a mobile member for automatically adjusting a machine. The eccentric actuator comprises a ferromagnetic drive force transmitting screw and nut (of larger diameter than the screw) to convert into axial movement the cycloidal rolling movement of the screw relatively to the wall of the fixed nut, the latter itself forming an integral part of means for converting an electromotive force into a displaceable magnetomotive force whose resultant generated flux causes mutual adhesion, as well as said cycloidal relative movement of the screw and the nut. The screw disconnects when supply current is cut off. The invention is applicable to the automatic control of a flap for regulating the temperature of the intake air in heat engines.