Which component is responsible for adjusting the air-fuel mixture in an engine?

The fuel injector plays a crucial role in adjusting the air-fuel mixture in an engine, which is vital for efficient combustion. In modern engines, fuel injectors are responsible for delivering a precise amount of fuel into the intake air stream. The electronic control unit (ECU) monitors various parameters, such as engine load and temperature, to determine the optimal fuel delivery, ensuring the right air-fuel mixture for different operating conditions.

While the throttle body controls the amount of air entering the engine, it does not directly adjust the fuel mixture but rather works in conjunction with the fuel injector. The intake manifold distributes the air-fuel mixture to the individual engine cylinders but does not control the mixture itself. The carburetor, found in older engine designs, mixes air and fuel but has largely been replaced by fuel injection systems in modern vehicles due to their efficiency and precision. Therefore, the fuel injector is the component specifically tasked with adjusting the air-fuel mixture based on real-time conditions, making it the correct answer in this context.