What symptoms may indicate a vacuum leak in an engine?

High idle speed and fluctuating engine RPMs are key symptoms of a vacuum leak in an engine. A vacuum leak occurs when there are unintended air pathways in the intake manifold that allow extra air to enter the engine beyond what the engine control unit (ECU) has intended based on the current fuel input. This excess air disrupts the proper air-fuel mixture and can lead to an increase in engine RPMs, resulting in a high idle speed.

Fluctuating RPMs happen because the engine's computer attempts to adjust the fuel delivery in response to the changing amount of air entering the cylinders, causing instability in operation. These symptoms can often be accompanied by other signs, such as rough idling or acceleration issues, indicating that the air-fuel mixture is no longer ideal for smooth engine performance. Recognizing these symptoms is crucial for diagnosing and addressing engine performance issues effectively.