What can a vacuum leak cause in an engine?

A vacuum leak in an engine can disrupt the air-fuel mixture that is essential for proper combustion. When there is an unmeasured influx of air entering the intake manifold, the engine's control system cannot compensate adequately. This leads to a lean mixture, meaning there is too much air in relation to the fuel.

As a result, one of the most noticeable symptoms is a rough idle, as the engine struggles to maintain smooth operation due to unbalanced fuel and air ratios. The engine has to work harder to compensate for the lack of fuel, which can lead to poor fuel economy as well. The efficiency of the combustion process is compromised, resulting in reduced performance and increased emissions. Collectively, these effects define the core impact of a vacuum leak on engine performance, making the observation about rough idle and poor fuel economy accurate and relevant.