I bet you have read
a hundred times or more
that a dirty air filter reduces MPG....

Recently both Hot Rod Magazine's technical guru Marlan Davis
in his 'Pitt Stop' advice column,
and now
Consumer Reports in actual real world tests
correctly state that on a modern EFI engine
dirty air filters don't affect MPG
unless they are super-severely plugged up:

http://www.consumerreports.org/cro/c...-406/index.htm

sample quote:

According to our tests, driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being used.

 

great info.
It made me reconsider getting a CAI. There was one listed on craigslist for less than half, new in box, but if its not going to help mpgs, then i don't need it.

 

since it is always better to test for yourself
doubters should consider a test
where they tape off part of their filter
and do a careful test...like with two trucks convoy style

if you don't wish to tape off a working filter
consider using a heavily clogged used one
like a dealership might give you if asked