@SkyWhisperer - I agree. Air inflow is important in a lot of ways for your car, and the air filter is just one place to look for. Another thing to watch out for is mass airflow sensors.
The mass airflow sensor monitors the amount of air going into the engine and it uses that information to regulate how much fuel your engine needs to run efficiently.
I found one easy way to check if the mass airflow sensor is working right – I just tap on the engine hose. If the engine stumbles, that means that there is a hiccup with the air inflow sensor. That’s the simplest method.
Of course mechanics have their meters and computers; that’s more precise, but this is the method I use before I ever take the car to a mechanic.