Method of reducing high cyclefatigue of turbochargers

A method of reducing high cycle fatigue of a turbocharger fitted to an internal combustion engine in which fuel supply to the engine is controlled by an electronic engine management unit (ECU) in accordance with a fuel map of fuel values required to meet different engine operating conditions. The method comprises varying the fuel value F associated with a particular engine operating condition to thereby prevent the turbocharger running at the same constant speed each time said particular engine operating condition arises.