Tyhjäkäyntikierros

Tyhjäkäyntikierros refers to the engine speed when a vehicle's engine is running but the clutch is disengaged and the transmission is in neutral. This state is also commonly known as idle speed or idling. The engine control unit (ECU) manages the tyhjäkäyntikierros to maintain a stable engine operation, typically between 600 to 1000 revolutions per minute (RPM) for most gasoline engines, though this can vary depending on the engine design and manufacturer. Diesel engines often have slightly lower idle speeds.

The primary purpose of tyhjäkäyntikierros is to keep the engine running without stalling while the vehicle is stationary or in neutral. This allows essential vehicle systems that rely on the engine's power, such as the alternator to charge the battery, the power steering pump, and the air conditioning compressor, to function. Maintaining a consistent tyhjäkäyntikierros is crucial for fuel efficiency and emissions control, as higher or lower than optimal speeds can lead to increased fuel consumption and pollutant output.

Modern vehicles employ various sensors, including those for engine temperature, manifold absolute pressure, and oxygen levels, to precisely control the tyhjäkäyntikierros. The ECU adjusts the amount of fuel injected and the timing of the spark plug to achieve the target RPM under different conditions, such as when the engine is cold or when accessory loads like headlights or air conditioning are applied. Problems with the tyhjäkäyntikierros, such as it being too high, too low, or fluctuating erratically, can indicate underlying issues with the engine's fuel system, ignition system, or emission control components.