As long as we’re on the topic of air filters, it seems logical to talk about the air duct system. This is especially critical on vehicles equipped with a Mass Airflow Sensor, or MAF. This is a sensor in the intake stream that actually measures the air going into the engine. The computer uses this measurement to calculate a fuel mixture. One thing to watch out for is air leaks in the tube that runs from the air filter box to the throttle body of the engine. Any leaks here allow unmeasured air to enter the engine. This unmeasured air, or “pirate air,” has not been accounted for by the computer. This means that you have air with not enough fuel mixing in the combustion chamber. When this happens, your engine can perform poorly and get poor gas mileage. So take a moment to look over the air intake system for any leaks. Also, make sure all the clamps and connections are secure and not allowing any extra air to enter the engine.