What causes fluctuating idle?

Fluctuating idle can be caused by various factors, including vacuum leaks, which allow unmetered air to enter the engine, disrupting the air-fuel mixture. Additionally, issues with the throttle body, such as carbon buildup, can impede airflow. Faulty sensors, such as the Mass Air Flow (MAF) or Throttle Position Sensor (TPS), may send incorrect data to the engine control unit (ECU). Lastly, problems with fuel delivery, like a clogged fuel filter or failing fuel pump, can also contribute to an unstable idle.