Definition: In a traditional spark ignition gasoline engine, the throttle body is the part of the air intake system that controls the amount of air that flows into an engine's combustion chamber. It consists of a bored housing that contains a throttle plate (butterfly) that rotates on a shaft. When the accelerator (gas pedal) is pushed down, the throttle plate opens and allows air into the engine. When the gas pedal is released, the butterfly closes and effectively chokes-off (throttles) air flow into the combustion chamber. This process effectively controls the speed of the engine and ultimately the speed of the vehicle.
By controlling air flow within an engine, the throttle body directly controls engine speed.
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