Check this page I found out. Some interesting things that go backwords with those stupid gas saving emails going out...

http://www.azcentral.com/business/consumer/articles/2008/06/09/20080609biz-GasMyths-09.html

Yep known that for a while. If you notice all my advice never included the "myths" The only one I don't buy is the dirty air filter. Yes the PCM will reduce the fuel to keep the proper A/F mix but at the same time the motor isn't at it's most efficient. So I believe in the long run you'll suffer at the pump. Same as using 87 octane in a car that is designed to run on 91. Just cause the sensors are there to adjust the timing to prevent knock all that does is save the motor. The motor is not operating at it's most efficient so you end up suffering in the long run as well.

Think of it this way is it way (generic numbers for ease of use)a motor is designed to be most efficient at say 1700 rpm at say 65mph that includes proper octane, full load of air into the intake properly operating O2 sensors and such. Now clog that air filter up or pull timing and to get the same oomph out of the motor it now has to turn 1900 rpms at 65mph. Which version would be more efficient?

How does a/c help with the gas mileage why you are on the highway?

well if you want to stay cool you have two options. A/C or window open. When on the highway the aero drag induced by the open windows requires more power to move the car at say 65mph then it does to have the windows up with the A/C on at 65mph. More power means more fuel. Aerodynamics/weight play a huge role in mpg. The slippery cd of the GP plays a big part in people averaging 29-33 mpg in the gtp.

Drag coefficient how I love thee, let me count the ways...

With a dirty air filter, your PCM compensates for less fuel. However, you get less power.

To compensate, you drive harder with higher RPMs Herc mentioned. This brings in more air/fuel that it would with a clean filter. This causes dirty air filter = less mpg.

LOL the more I thought of the dirty airfilter blurb by the guy who wrote the article made me chuckle. If less air in the motor means less fuel maybe we should take off our free flowing filters and put the most restrictive one on and fill it full of dirt.

Written with sarcasm.