Abstract: An auxiliary apparatus or device for attachment to an internal combustion engine, so that at a certain point in the depression of the accelerator pedal, an increased resistance to further depression of the pedal is abruptly encountered. This point is constantly adjusted in accordance with the engine vacuum so that when engine vacuum is high, considerable depression of the pedal is permitted before the resistance is encountered, and conversely when the engine vacuum is low, the resistance point is soon encountered. This is effected by attaching one end of a cable to the throttle mechanism of the engine and attaching the other end to a vacuum actuated bellows. When the slack in the cable is taken up, added resistance is provided in the form of a loading spring, which requires increased foot pressure against the accelerator to overcome.