Abstract: The speed control actuator can be used to modify a control linkage fitted between an accelerator pedal and a carburetor or fuel injection pump on a vehicle engine. The actuator includes a forked lever which is mounted for rotation on the shaft of the fuel regulator, and a pulley which is mounted for rotation relative to the forked lever. The accelerator pedal is connected by means of a cable to the forked lever. Another cable passes over the pulley and is connected to a microprocessor controlled cable drive. The cable is advanced and retracted, in accordance with a vehicle speed related signal, to adjust the fuel regulator independently of the accelerator pedal. A preferred form of drive means is also described which employs a microprocessor producing a speed-related output in the form of a pulsating current of one polarity or another, and having a variable mark-to-space ratio, for driving a dc motor coupled to the actuator.