It takes more than simply a tank of fuel to bring an engine to life. Before that fuel can release its energy it must be combined with air. The resulting mix can then be ignited using a carefully timed high-voltage spark.

To achieve optimum combustion in every cylinder under all load conditions, modern engines are equipped with a range of actuator devices which are under the direct control of engine management system. One of the key functions of these devices is to maintain a constant idling speed despite varying demands made by the air conditioning or other electrical systems.

However, a number of faults can still occur that may adversely affect the air/fuel mix. Actuator components can become soiled or seized, which short circuits in the ignition coil can undermine performance. Other potential problems include faulty electromagnetic drive components or a loss of power to individual devices. In each of these cases, it is usually advisable to replace at least one actuator component.