Regular maintenance on a 2000-2006 (E46) BMW M3 is very important, but going to a dealership or certified technician can be expensive. So why not do some of it yourself? Replacing the air filter in the engine, for instance, is a simple, not too invasive, and low-risk job for anyone looking to save the $100+ that a dealer might charge to do the job.
Note: This guide may not apply to the installation of an aftermarket air filter.
Identify the two plastic clips on the left side of the box. These clips consist of small plastic hooks on the lid hooked into square holes attached to the base.
To remove these, press the left side of the lid down and pull up slightly on the right side. While doing this, gently slide the lid to the right.
If done correctly, you should now be able to see the rubber gasket of the air filter (most likely it will be bright orange).
Be careful not to lift or bend the lid too much! You will be able to lift the lid up to a certain degree, but remember that it's still attached to the intake and the air flow sensor; putting too much force on either will destroy them.
Take the new air filter and, while gently lifting the air box lid, slide the new air filter in until it seats flat inside the box.
Hold the new filter by the orange gasket only; avoid touching the actual filter part as much as possible.
The new air filter might be slightly different from the one removed, as some filters have cotton pads on the bottom while some do not. Both styles of air filter are acceptable.
To put the lid back in place, press down on the left side of the lid and pull up slightly on the right side while sliding the hooks back into the holes.
This might take several tries, as the new filter's gasket might be slightly larger than the old one, making it difficult to slip the lid back into place. You may need to use the flat head screwdriver to press the gasket under the lid. If the hooks are in place and the gasket isn't showing, the lid is in place.