You definitely have an issue. I have an 04 with 70,000 on it and right now in the winter I get about 33-37, summertime I get 38 +. I had one tank I got 45! (5 speed)

Check your air filter for grins. I checked mine not too long ago and haven't had the car too long, and it was also bought 'honda certified' and it was full of crap.

Worth a try! Maybe you got some crappy gas going on too. My mpg went down a bit with some crap gas I got.

 

Yeah, that's not normal, stock airbox or not. I used to get 37 with my 01, when it was stock.

check/ replace air filter, check tire pressures, and you may need to replace one or both o2 sensors. Probabaly unlikely (unless your car feels slugish), it could also be a clogged catalytic converter, which would be a result of a bad o2.

 

for 28xxx miles is pretty low to check these.

Replace fuel filter
Spark plugs (ngk)
air filter

These should add up right under 40 bucks id do this and then check your milage, and most hondas have been known to have "bad" gas needles as they can be unaccurate and you will want to go by your odometer

 

I would really check that air filter first for grins. Auto or stick, these Civics should get 30+mpg almost all the time if you drive them without going WOT all the time.

 

You cant guess that its halfway, you have to let it run as far down as possible. Then that wouls be closer to the real mpg.