How many miles / often should this be replaced?

Where can I order some online?

Has anyone made any videos on how to DIY?

Thanks in advance.

 

3 years or 30k miles. You can buy them online from several sources. Rockauto and Ebay are two examples. Here is a listing of some available from Rockauto :
http://www.rockauto.com/en/catalog/l...ir+filter,6192

They have AC Delco professional for 7 bucks and all the way up to a factory Denso for 17 dollars apiece. Remember that there are two air filters in our LS's

 

I always go with K & N air filters. Buy the cleaning kit at the same time. All my vehicles have them. You will get about 1 mpg better and 10 hp. with them. I clean them with a dry paint brush and a can of air about every 15K, and a wash them every 50K.

 

You no doubt got those figures from K&N. Ive read numerous neutral party tests and in most cases there was no increase...and in some (a Scion tc), there was a loss in power. In addition, there's information that MAFs can foul as well as allowing sand in your oil. My oil analysis after running K&N showed excessive sand in my oil sample. This disappeared after replacing it with a quality paper filter.

These filters have been discussed at length in this forum, there are still a couple of K&N users, but not many.