What effect does a dirty air filter have on vehicle performance?

A dirty air filter primarily restricts airflow into the engine, which is crucial for proper combustion. When the filter becomes clogged with dirt and debris, the engine receives less air than it requires for optimal performance. This reduction in airflow can result in a rich fuel mixture, where too much fuel is present compared to the amount of air. As a consequence, the vehicle may experience decreased fuel efficiency and overall performance. The engine may struggle to operate at its best, leading to issues like sluggish acceleration and reduced power output. Therefore, the impact of a dirty air filter is significant, affecting both fuel economy and engine efficiency, which is why the correct choice highlights its detrimental effect on fuel economy due to airflow restriction.