The air filter's role in a vehicle is to let fresh air flow all the way through the system to mainly help with the burning process, without letting debris and dust inside. The stream of air will be mixed with the fuel to produce an air-fuel mixture which will be burnt to produce force for the car to move forward. Too much air is unnecessary since the amount of fuel pumped in is fixed. Conversely, if there isn't enough air inside, the air to fuel ratio will be imperfect and the outcome of the combustion process will be less then ideal.

Even though this device can be easily replaced or cleaned, most people still forget to take care of it periodically. The manufacturer's recommended number is 12, you should replace it in either 12 thousand miles or 12 months. This number can changes, depending on the environment of where you live. As a rule of thumb, you should take your car to an auto service more frequently if your area is crowded and packed with industrial sites, and vice versa. Since this device is made of layers of hardened papers, the cost of replacement is relatively low. You can still wash it if you want to.

Below are some signs of a troubled air filter and it can vary from vehicle to vehicle. Your vehicle can have one or all of the following symptoms.

1. Black exhaust fume
The exhaust fume turning black translates to too much fuel in the air-fuel mixture ratio. When this happened, the excessive amount of fuel will be partly burned, thus producing this color. In other words, there's less air than usual in the mixture, meaning your filter might be clogged.

If this has happened to your car, there may be too much oil in the burning chamber

2. Harsh Engine sound
When the engine cranks harshly and produces an unusual sound, the reason might lie in the spark plug. This can be traced back to, again, a clogged air filter. The aforementioned black exhaust fume could leave a trace of carbon soot on the spark plug that prevents it from firing properly.

3. Gunshot sound from the exhaust pipe
If there's a banging sound when you rev the engine, the reason might be the fuel-air mixture again. Rich content of fuel in the mixture sometimes cause explosions, not combustion. The combustions inside the engine should be minor and more gentle.

4. A decline in fuel economy
It's only common sense when your car burns the same amount of fuel but travel less distance (excessive fuel burnt doesn't convert into energy), the fuel economy will consequently decrease.

https://www.youtube.com/watch?v=5lkX8aOuGSg
Clean Air Filter increase mileage and performance​

5. Oily smell emitting from the exhaust pipe
Sometimes you can smell a hint of oil smells when starting the car, and that's fine. But when you have traveled for some minutes, you stepped out of the car and detect a sharp smell of gas, your air filter might be the problem here. Excessive fuel resulted from a clogged filter that's not burnt completely will leave a trace of oily smell around the exhaust pipe.

In this case, the excessive oil cannot be burn completely and trickle down through the pipe to the road
When you see all or one of the above signs, our recommendation is to always change the filter because you could never clean the filter thoroughly and besides, it's so cheap it's not worth the effort of learning.
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[img]https://naijauto.com/car-maintenance/5-most-common-problems-from-a-clogged-air-filter-983[/img]