I picked up a Civic 2005 ex special edition last november.....I was getting like 330 miles to a fill up and it was all nice. Until recently its been terrible...230...260...nowhere ever over 300. Not even highway...i have gotten oil changes regularly and have about 10000 miles....i have no idea what it is...help thanks

 

It's under warranty...take it back to the dealer and have them inspect it.