Question: how do you know when you need to change your air filter?
Answer: Air Filter Looks Dirty. A new air filter will be white or an off-white color. ... 
Check Engine Light Turns On. The Check Engine Light can come on for many different reasons, and sometimes it is due to the air filter. ... 
Lower Horsepower. ... 
Black, Sooty Smoke Leaving the Exhaust Pipe. ... 
Smell of Gas When the Engine Starts.