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Alright. I was just getting ready to make a post, but since this one is on top, I'll add to it. I've been getting increasingly ****ty mileage, and at today's fillup was 23.4mpg. I do mostly city driving, short trips of 7 miles 4x a day - so that's expected that the car will not be warmed up and efficient. This time, I had about 75 miles of interstate driving too, so it should be better. I'm usually in the 26-28mpg range, but have been on a downward slide.

I've also been noticing that the car seemed a little "bogged down" occassionally, like it was slightly overfueled. The car has 64K on it (2002 GLS A/T), plugs and wires were replaced at 56K. Plugs are NGK Copper, wires NGK. Air filter is K&N drop-in panel, cleaned about 10K ago. I was thinking of getting a new set of plugs (better than NGKs bottom-end plug) and maybe throwing an OEM air filter on and seeing what happens. Any other things I'm not thinking of? My fuel filter could probably use replacing, but I'm not sure that would lead to poor mileage and what seems like minor-overfueling?
 

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Basic list for mpg: driver lead foot, spark plugs/wires, fuel quality, 02 sensor, tires
In my case:

driver: fine
spark plugs: questionable, not very old though
wires: fine
fuel quality: have tried different stations and brands, no difference
O2 sensor, unknown - is there an easy way to check it without special tools?
tires: brand new
 

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So get this. I'm on my way home to lunch and I decide to mess with the fuel mileage - I have the tib multigagues so I can see current fuel consumption in L/100KM. I set the cruise on flat level ground, going 45mph. Consumption = about 9.5 L/100KM (24.75mpg). I turned off the defrost. Consumption = about 6.5 L/100KM (36.18mpg).

Now we all know that running the defrost runs through the AC system. AC lowers gas mileage, but by 12mpg!?!

I repeated this test several times, turning defrost on and off and watching the needle bounce between the 2 points steadily. This could explain why it seems as winter goes on, I get worse mileage - I've been using defrost more.

I know a lot of you will say just turn off the AC button, but it doesn't work like that on my particular car. When I turn the defrost on the AC button doesn't light up, and pushing does not change anything (engaging or disengaging of the clutch on the AC). My old HVAC did work like that, but this one (I put LEDs in a second unit from Ebay) does not.

Opinoins, thoughts, suggestions?
 
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