A car’s throttle is essentially what controls how fast the engine goes, and therefore how fast the car goes. The throttle is usually a butterfly valve assembly on the intake manifold, and is connected to the accelerator, or gas pedal, via the throttle linkage. This linkage enables you to control the engine’s throttle by how far you move the gas pedal — the further down you press the gas pedal, the more the throttle opens.
Many people hold the misconception that the purpose of the throttle is to control the amount of fuel going into the engine. In fact, it is the exact opposite: the throttle controls the amount of air that goes into the engine.
An internal combustion engine runs on the force of exploding fuel and air. However, to generate the proper explosion in the combustion chambers, there needs to be a very specific mixture of vaporized fuel and oxygen. Therefore, in an internal combustion engine, there are several systems in place to regulate the air/fuel ratio.
In a carbureted car, the carburetor uses very simple principles of vacuum to maintain the correct air/fuel ratio. In a fuel injected car, on the other hand, the air flow meter, oxygen sensor, and the computer that run the electronic fuel injection all work together to ensure that the engine gets the right amount of both air and fuel. There are two different kinds of electronic fuel injection: throttle body injection, which works more like a computerized version of a carburetor, and multiport injection, which features a separate fuel injector for each cylinder.
Whether the car is carbureted or fuel injected, when the throttle opens, more air rushes into the engine. At the same time, the intake and fuel systems compensate by adding more fuel to the mixture. In other words, the throttle directly controls the amount of air that enters the combustion chambers, which indirectly affects the amount of fuel that enters the chambers.