What is a common symptom of a vacuum leak in an engine?

A common symptom of a vacuum leak in an engine is rough idle. When there is a vacuum leak, additional air enters the intake manifold beyond what the engine control unit (ECU) expects, which disrupts the air-fuel mixture. This alteration can lead to an imbalance in combustion, causing the engine to run unevenly or roughly at idle.

Furthermore, during idle, the engine requires a precise air-fuel ratio for smooth operation. Because vacuum leaks introduce excess air without a corresponding increase in fuel, the mixture becomes too lean, resulting in erratic engine behavior. This can be accompanied by symptoms such as fluctuations in engine speed or stalling.

Recognizing rough idle as a symptom of a vacuum leak is crucial for diagnosing engine performance issues. Addressing the vacuum leak can restore proper air-fuel mixture balance, leading to smoother idle and overall engine performance improvements.