When the air filter in your car becomes too dirty, it will clog and the engine will not be able to draw enough air into the combustion chamber. This can lead to a number of problems, such as a drop in power, a decrease in fuel efficiency and difficulty starting the vehicle. It can also cause permanent damage, including engine failure. One of the most common issues you'll encounter when you need to change your engine's air filter is decreased fuel consumption.
You can visually check the engine air filter to see if it looks dirty or if it is full of debris. If you've driven more than that since the last time you changed your air filter, it's probably time to change it. The cabin air filter also needs to be replaced regularly. Just because it doesn't directly affect your vehicle moving from point A to point B doesn't mean you should delay buying a new one or not replacing it at all.
Ignoring it can cause some rather uncomfortable effects, such as condensation on the windshield and poor air quality for people with allergies or breathing difficulties. The location of the air filter varies by vehicle, so consult your owner's manual to find out exactly where the filter is located. Be sure to monitor your air filter and replace it when you start to notice signs that it is clogged, and keep your car in perfect condition for as long as possible.