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Your Throttle (throttle body) worn out? » Read more about common malfunctions • Repair • Replacement manual
Air for the engine with the throttle valve
The throttle valve is controlled by the driver by way of the accelerator pedal. It regulates the amount of air which is let into the engine. By the valve's angle position and assisted by data from the throttle valve potentiometer, the control unit calculates the correct amount of fuel to be injected.
Throttle valve: construction and position
The throttle valve is located in the intake manifold directly in front of the intake valve, optimally fitting into the intake manifold's diameter. The valve rotates via a transverse axis, actuated by the throttle positioner. In the past, cables and return springs were used for this. Nowadays, in most cars a servomotor takes on this function.
Throttle valve function
Transversely to the air flow, the throttle valve can change its position from 0° to 90°. In the zero-position the intake manifold is closed. In the 90° position it is fully opened – the driver "stepping on it". The throtte valve is connected to the throttle valve potentiometer, transmitting the information on the angle position to the control unit. With these data the control unit calculates the amount of fuel to be injected. The engine always receives the optimal air/fuel mix. This is important for fuel efficiency. Furthermore, this construction mode ensures that no excess fuel enters the catalytic converter. If a deflagration occurs in the "cat" as a result of unburnt fuel, this almost always immediately destroys the component. This will cause the car to fail MOT inspection and an expensive replacement is necessary.
Throttle valve defects
The throttle valve is a delicate mechanism, particularly sensitive to pollution. If the air filter is defective or absent, dirt particles penetrate the valve's rotation mechanism and jam it. The driver notices reluctant acceleration and deteriorating driving comfort. The engine idles irregularly and the control unit reports errors. This can lead to the engine switching in failsafe mode. Particularly problematic are diesel engines with exhaust recirculation. For reduction of the nitrogen oxide, the combustion temperature in the engine is reduced. Already burnt exhaust is conducted back into the combustion chamber by the EGR-valve. The exhaust passes the throttle valve as well, gradually polluting it. The consequences are similar to those of a defective air filter: the throttle valve jams.
Throttle valve repair
The throttle valve is generally built in such a way that it can be removed and cleaned. Nowadays, many solutions are available. Yet, disassembly of the throttle valve is very complicated. We therefore recommend to leave the cleaning to a professional service provider. This will give you an adequate result or alternatively information on whether the component is salvageable. When the valve needs replacement, it has to be programmed into the control unit. We also recommend replacing the servomotor as well as the potentiometer. This will give you a fully new component group, set to operate for the next 50.000 km. If the budget allows it and the spare parts are not too expensive, a full replacement of the entire throttle valve and accessories is the most sensible thing to do.
Throttle valve costs
Throttle valves are mechanical components, consisting of an aluminium housing and an internal metal valve. The housing is made in a die-casting process, requiring precision tools for its postprocessing and assembly. This severely limits the number of companies able to manufacture this component. As a result, throttle valves as original part or spare part are available at relatively few manufacturers, making its price as a new spare part high. The price for a new throttle valve starts at 150 EUR (± £130). The ca. 80 EUR (± £70) for a servomotor and a potentiometer come on top of that. All in all this component group is one of the more expensive units. Therefore a cleaning attempt is almost always worth while.