Most automobile owners are aware that a filter is used to capture and remove the dirty air particles from the outside air that leads into the engine combustion compartments. In the vehicles of today you have two commonly different types that are being used, paper and a K&N filter.
The paper filter is just that, a filter that is made out of paper products (in most cars). The K&N filter is made of a mesh with a cotton filter medium and coated with light oil to aid in the capture of the dirt particles. Both products work great when used in the proper context for which they are designed.
The Problem
Paper filters are designed to capture the dirt through the paper and can be plugged fairly quickly. It is advisable to check your air filter at least every 10,000 miles or so. When it becomes dirty you just replace it with a new one.
K&N filters are designed to capture the dirt just like a paper filter but do not become plugged as quickly. When they do, you just remove them, wash them out with a little soap and water, spread on a light oil and re-install. The problem is that the oil can cause problems in the newer cars today because of sensors placed between the filter and air intake. If the filter has too much oil applied it can get on the sensor, causing your engine light to come on. For most people this is a trip to the automobile mechanic to diagnose the problem.
Solution
If you car is a newer 90s or later, stay with the manufactures type of filter unless you are a backyard mechanic that really knows what he / she is doing. If you are using a K&N filter, do not over oil the filter and make sure to remove any excess.
Experience
I am one of those backyard mechanics that thought I knew what I was doing. About 6 months ago I put a K&N filter in my Izusu Rodeo (my wife's car) to save money on the cost of the paper filters. This last week my check engine came on and the reason, you guessed it; the oil from my air filter plugged the sensor going into the engines intake.
I have always used K&N filters on my vehicles to aid in the air flow to the engine and over the long haul reduce air filter costs. After the trip to the auto dealer to find out what caused the engine light to come on and being a little embarrassed, I just went back to paper on the Rodeo. I still use fibrous filters on my truck, motorcycles, and dune buggy.
