A throttle body comprises a valve that is used to control the amount of air entering an engine, and therefore the amount of petrol admitted from the carburettor or by the injectors.
On a fuel-injected engine the throttle body is normally located between the air filter and the intake manifold, and is connected via a cable to the throttle pedal, or gas pedal, inside the car.
When the driver presses the pedal a butterfly valve moves to let more air flow into the manifold. The airflow sensor detects more air and sends a message to the car’s ECU to boost the amount of fuel being supplied by the injectors.
On older-style engines, the throttle is part of the carburettor, and is positioned below the venturi, where fuel is mixed with air.
Most autos have just one throttle but larger-engined cars can have one for every cylinder - they sit above each cylinder - although these are relatively uncommon.
A healthy air filter is absolutely critical to the operation of the throttle body, because dirty air can cause a build up of pollutants on its inner surface, which over time will interrupt the air flow.
After disassembling it, clean the throttle body with a suitable solvent or carb cleaner, paying particular attention to the throttle plate, using a toothbrush, pipe clear and cotton cloth.
Other throttle body problems include faulty speed/distance or MAP sensors, which send signals to the ECU and cause the engine to stall when the car comes to a standstill or an erratic idle.
An engine that revs too high at idle can be caused by an incorrectly adjusted throttle stop or a vaccum leak in the hoses that connect to the throttle body.