Here's a simplified explanation:
* Idle speed: Modern cars have an idle system. This system maintains a minimum engine speed even when you're not pressing the gas. The engine needs this minimum speed to keep running to generate enough power for things like the alternator (charging the battery), power steering, and other accessories. This idle speed is controlled electronically.
* Throttle position sensor: A sensor detects how far you're pressing the gas pedal (the throttle). This sensor sends a signal to the engine control unit (ECU).
* Engine Control Unit (ECU): The ECU is the "brain" of the car. It receives information from various sensors, including the throttle position sensor. When you're not pressing the gas, the throttle position sensor indicates a closed or nearly closed throttle.
* Fuel Delivery: Based on the throttle position and other sensor data (like engine speed, oxygen levels, etc.), the ECU determines how much fuel to inject into the engine. If the throttle is closed (no gas pedal), the ECU reduces fuel delivery to a minimum, just enough to maintain the idle speed.
* Engine Stall: If something goes wrong—a sensor failure, a problem with the fuel system, a mechanical issue with the engine—the ECU might not be able to maintain the minimum fuel delivery necessary for idle speed. Without enough fuel, the engine will stall and turn off.
In short, it's not that the car *automatically* shuts off; it's that the system is designed to only supply the bare minimum fuel needed for idling. If the demand for power exceeds the minimum supply (e.g., you're asking for more power without pressing the gas, there's a problem with the electrical system, or the engine is struggling), it will stall.
