Which part of the vehicle is responsible for stopping the flow of air and fuel in fuel injection systems?

The throttle body plays a crucial role in a vehicle's fuel injection system by controlling the flow of air and fuel that enters the engine's intake manifold. Specifically, it is responsible for regulating the amount of air that passes through it, which in turn affects how much fuel can be injected by the fuel injectors. When the throttle is closed, it restricts airflow, and thus the engine receives less air and fuel, effectively stopping the flow to some extent during idle or when decelerating. This dynamic is essential for maintaining proper engine operation and response to the driver's input on the accelerator pedal.

In contrast, the injector nozzle is responsible for spraying fuel into the intake manifold but does not have direct control over the air intake. Similarly, the fuel return line is part of the fuel delivery system that allows excess fuel to return to the tank, and the fuel filter protects the fuel system from contaminants but doesn't regulate the air/fuel mixture. Therefore, the throttle body's function of controlling air flow demonstrates why it is the correct answer to the question regarding stopping the flow of air and fuel in fuel injection systems.