Audi Workshop Service and Repair Manuals

With the electronic throttle system, the throttle valve is not actuated by way of a cable in response to the position of the accelerator pedal. There is no mechanical link between accelerator pedal and throttle valve.

The position of the accelerator pedal is signalled to the engine control unit by two accelerator pedal position senders (variable resistors in a joint housing) which are connected to the accelerator pedal.

The accelerator pedal position (driver input) is one of the main input variables for the engine control unit.

The throttle valve is operated by means of an electric motor (throttle valve actuator) in the throttle valve control part over the entire engine speed and load range.

The throttle valve is operated by the throttle valve actuator as specified by the engine control unit.

With the engine stopped and the ignition switched on, the engine control unit regulates the throttle valve actuator precisely in line with the specifications of the accelerator pedal position sender. In other words, when the accelerator pedal is depressed halfway the throttle valve actuator opens the throttle valve to the same extent and the throttle valve is then roughly half open.

When the engine is running (under load) the engine control unit can open and close the throttle valve independently of the accelerator pedal position sender.

It is thus possible, for example, for the throttle valve to be fully open although the accelerator pedal has only been depressed halfway. This has the advantage of avoiding throttling losses at the throttle valve.

Under certain load conditions, this system also results in considerable improvements as regards pollutant emissions and fuel consumption.

It would, however, be inappropriate to think of the electronic throttle system in terms of one or two components. On the contrary, it includes all the units needed to help determine, control and monitor the position of the throttle valve (e.g. accelerator pedal position sender, throttle valve control part, EPC warning lamp, engine control unit...).