[mwebb]

http://www.fueleconomy.gov/FEG/pdfs/...02_26_2009.pdf

sorry people
this is the latest of three sets of test results that all show the same thing

clogged or restricted air filters have ZERO affect on fuel economy

quoted from the EPA TEST RESULTS Feb 26 2009
"Despite the filter restrictions, however, no significant changes in fuel economy were observed. Each vehicle was run through at least three rounds of FTP, HFET, and US06 tests with the new air filter, and the same protocol was repeated with the clogged air filter. The tests were conducted on consecutive days for each vehicle. This format was used to allow for the required soak time to perform a cold FTP each morning. The resulting fuel economy data for the vehicles are shown in Figs. 3.8, 3.9, and 3.10. Range bars in the figures show the minimum and maximum of the tests for each case, while the columns show the average. Test-to-test repeatability is within about 1.5%, and all of the variances between the new and clogged air filter cases are similarly within about 1.7%. The baseline fuel economies for the vehicles were all within 0–6% of unadjusted EPA certification database values (US Environmental Protection Agency) for similar vehicles.
The changes observed by clogging the air filter produced no significant effect on the fuel economy of the vehicles tested, when tested over these three standard cycles that represent a wide range of driving conditions. It is possible that there may be some isolated operating conditions under which the fuel economy may be more susceptible to a clogged air filter. However, such operating conditions are not likely to be consistent from vehicle to vehicle. The three driving cycles used here are representative of a wide range of driving conditions, as described in Sect. 1."

read this if you want ,
believe or not - as you choose -
see section 3.1.3 for test results and discussion on FE