robfriedenberger said:
Well you installed a KN CAI, more air means more gas to get the mixture right, you may want to clean your TB, But usually factory setup is best for MPG. Also how are you testing this ? Resetting the trip meter when you fill up? Also blends of gas can cause bad MPG, being its starting to get cold you maybe working with differnt gas.
Do you have a tune or did the PO have a tune?
I searched K&N's FAQ's and Question Number 1 was "How will a K&N filter affect my vehicle's fuel economy?":
K&N's Answer: 1. How will a K&N filter affect my vehicle's fuel economy?
There is a relationship between air filter restriction and mileage. The theory behind this is simple, the harder an engine has to work to suck air through the intake tubes and air filter, the more gas gets wasted in the process. Many K&N users report an increase in their fuel economy after beginning to use our air filters, as noted on our testimonial page. However, these experiences do not mean you will also experience a change in your mileage. We certainly understand why it is theoretically possible for a consumer to experience a mileage increase after installing a K&N air filter or intake system, however, we do not go so far as to make a general claim that our air filters and intake systems will provide an increase in mileage.
It is virtually impossible to make sweeping and general claims about mileage. Even the EPA fuel rating numbers for new cars are often not representative of the mileage you actually experience. There are many variables that affect mileage such as: tire inflation, the type of fuel, weather, elevation, the speed at which you drive, the gear in which you drive, the speed with which you accelerate, engine maintenance, excessive idling, cruise control, the grade of motor oil you use, and of course, the condition of your air filter. In short, mileage is complicated.
K&N filters are less restrictive than disposable paper or synthetic air filters and K&N Intake Systems are less restrictive than the factory installed air path. So K&N filter technology could be an important tool, when combined with other elements, to help keep mileage as high as possible.
Oh yeah, there's one more limitation imposed by science. If you take advantage of added power by driving more aggressively, you will reduce mileage. You cannot have your cake and eat it too.
http://www.knfilters.com/faq.htm#1
Hope this was helpful! If not, I recommend calling K&N directly and see what answer they supply you with.
Good luck!
Tom
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