My 2012 Honda Fit had been getting 35 mpg hwy 28 city. Suddenly im getting 18 mpg! Took her in for an oil change and had my mechanic check, he sees nothing amiss ( wheels not locked up, tire pressure okay, spark plugs changed within the last year). Anyone else? No engine code.

 

Check to see if your plugs are making a run for freedom. They do that .. :/

 

I second this. Any funny clicking, or sounds like yer blowing into a jug syncing up with cylinders firing?coming from the engine ofcourse. Could prolly just feel up the little bolts holding down the coils/plug wires onto the spark plugs. If it spins, you know, but even if it doesnt I'd still check the plugs since its such a big deal. I bet theres several other symptoms not mentioned, yeah?
We're looking for a significant problem here so I'd advise using uber until this is resolved

 

As I transitioned away from a 'road warrior' to a more local driver working from home, my MPG (s) gradually dropped over time. I'm sure some component of this is due to the car aging / getting out of tune. Although I changed the plugs (really didn't need to) when they came loose thinking that maybe it was due to the crush washer, I haven't adjusted the valves yet. I have changed the the AT fluid (12 qts process) twice at 30,000 mile interval. I also started running a 205/50-16 tire on a 16x7 wheel and a catback, and those would have some impact too on MPG. The weird line shape last summer was due to not driving it much at all while I used another vehicle more often (fewer fill ups = fewer data points).

 

I will say that (In my experience) the Fit doesnt idle well, as in it uses a lot of gas idling. When I drive 1 mile in heavier traffic, my fuel economy goes to shit. but drive on the interstate and i easily get over 34 MPG. I average about 24-27MPG because I do so much city driving. But I went out to the cape a week ago and that was the first time I have had a 30+mpg tank in a long time. If this ISNT normal, let me know. but its been like this since I bought it.