Tyhjäkäyntipiiri

Tyhjäkäyntipiiri is a Finnish term that translates to "idle circuit" or "idle system" in English. It refers to a component or set of components in an internal combustion engine that are responsible for maintaining a stable engine speed when the engine is not under load, such as when the vehicle is stopped with the engine running. This system is crucial for preventing the engine from stalling and for ensuring smooth operation at low revolutions per minute.

The primary function of the tyhjäkäyntipiiri is to control the amount of air that bypasses the throttle plate when it is closed. When the driver is not pressing the accelerator pedal, the throttle plate is mostly closed, restricting airflow. However, a small amount of air is needed to keep the engine running. The tyhjäkäyntipiiri manages this airflow. In older vehicles, this was often achieved through a manually adjustable screw or a simple valve. Modern engines utilize more sophisticated electronic control units (ECUs) to manage the idle speed.

Electronic tyhjäkäyntipiiri systems typically employ an Idle Air Control (IAC) valve or a similar actuator. This actuator can precisely adjust the amount of air entering the engine, allowing the ECU to fine-tune the idle speed based on various factors such as engine temperature, air conditioning load, and transmission gear. This electronic control ensures optimal fuel efficiency and emissions control during idling. Issues with the tyhjäkäyntipiiri can manifest as rough idling, stalling, or inconsistent engine speed.