decreasing mileage on 05 CROWN VIC COP CAR

This is by far the best Crown Vic knowledge base online...hoping someone can give me some leads to follow on a problem I\\'m having.

Have a \\'05 Crown Vic POlice Interceptor package car, 120K miles, in great shape body & mechanical. Bought it from a buddy in April this yr and was getting around 16MPG in city/ 23-25 MPG on hwy even thru mid July in hot weather and running the AC.

Toward end of summer I replaced fuel filter with a high end FRAM one..my mechanic when he took old one out said this one was prolly original one, so i figured I did a good thing..figured MPG would get better..WRONG...mileage has went down to 12-13 MPG and 20-21MPG hwy

My guy has checked plugs/wire/air filter etc...everything good there..have gotten my gas at lots of different stations and retailers to see if i\\'m getting bad gas..no difference...

My ?: is not putting a Motorcraft fuel filter in the difference, even tho I put a top line FRAM in?....I had an old HOnda once where my guy recommended cheaper plugs that what Honda called for as they actually worked better and got better mileage for you, even tho they were basically entry level plugs...or is there other things I should have him check other than what I mentioned?......thanks in advance..Terry

I do not know what your exact problem is but...I just recently cleaned my throttle body with CRC Throttle Body Cleaner and what a difference it made! I also have an 05, when I cleaned it, it was noticeably quick and more responsive. Also rough idle went away. I have about 103,000 miles on it now. I think my mileage has improved but I will find out tomorrow. Maybe your mechanic can dig that old filter out of the trash...

I also have a 2005 P71 with a recent Fram fuel filter change. I\\\\\\'ve lost about 3-4MPG the last 2 months, I do a lot of city driving. I\\'m getting 13-14 MPG, I just chalked it up to the extremely cold temperatures, extended warm up in the morning for quicker interior heat, extra trunk weight for winter driving and even winter blend fuel this time of year.
It been a much colder winter than normal here in Pennsylvania, but maybe our cars don\\\\\\'t like Fram Fuel Filters ??? The general consensus at CrownVic.net is 13-14 MPG city is about right for my situation. Best of luck - Bill Miller