What engine issue is commonly associated with a vacuum leak?

A vacuum leak in an engine typically leads to an improper air-fuel mixture, causing the engine to run lean. When there's more air than fuel entering the combustion chamber, the engine struggles to operate efficiently. As a result, this imbalance can lead to various performance issues, with poor fuel economy being one of the most significant symptoms. The engine compensates for the lack of fuel by adjusting the fuel injection, but this often results in inefficient combustion and an increase in fuel consumption relative to the power produced.

While vacuum leaks can indeed cause a high RPM idle due to the engine controlling the air intake, poor fuel economy is a more direct and universally recognized consequence of such leaks. High RPM idle may also be associated with other issues such as throttle control problems, making it less specific in connection to vacuum leaks alone. Thus, the identification of poor fuel economy as a common issue directly illustrates the impact of a vacuum leak on engine performance.