Replace your air filters
Told that your engine air filter needs replacing? It may be true. But testing your filter is easy and replacing it is a brainless task—so do it yourself. Replace the filter based on its actual condition rather than the manufacturer's recommended service intervals. Checking its condition isn't rocket science. Just pull it out and give it a look-see (photo 2). If it fails the back-light test, replace it. While the filter is out, vacuum out the crud in the air cleaner box.
Video: When to Change an Air Filter
A dirty air filter can decrease your gas mileage by almost 10%. Rick Muscoplat, an automotive expert at The Family Handyman, will show you how to test and when to change an air filter and start getting better gas mileage.