In a rotary actuator (1) with rotary slide valve (3) for controlling a throttle cross-section, the sealing of the pneumatic (16) and of the electrical part (17) is to be improved. For this purpose, the shaft (11) is supported twofold, both on this side and on the other side of the rotary slide valve (3). Both roller bearings (13, 14) are located in a one-piece housing (12). As a result, the tolerance-related width of the air gap between rotary slide valve (3) and control opening (6) is reduced, on the one hand, and, on the other hand, an isolating seal between the parts (16) and (17) is formed by the bearing (13). The rotary actuator (1) is particularly suitable as idle-speed rotary actuator for internal combustion engines.