A fuel economy unit (30) is disclosed for an engine system comprising an internal combustion engine or electric motor having a demand input, an output member drivable by the engine, and a user-operable demand control (13) for providing a demand signal (P1,P2) coupled to the engine demand input to control the engine output. The fuel economy unit receives an input signal (D) indicative of acceleration of the output member, or from which acceleration of the output member can be derived, and modifies the coupling of the demand signal to the engine demand input in dependence on the acceleration of the output member to limit the acceleration of the output member.