The Eclipse is averaging around 18mpg on a good day with no wind and a nice 75degree climate.

So, i'm thinking change the fuel filter,and an induction flush, and that might help a little.

anyone else concur?

 

Might want to check for leaking injectors, not sure if it would kill gas mileage that much but never know. If you dont have a gas smell, then there shouldnt be any fuel line leaks. Good luck.

 

do a general tune up, including the pcv valve and intake filter (if it looks bad)

 

I agree with a general tune up. Plugs, wires, air filter, and PCV (TE). I run of Seafoam wouldn't hurt either.
After the Seafoam (if you do it), get new upstream o2 sensors. They play a big factor gas milage, also, if your cat is clogged or is becoming more of a bottleneck then it can be a contributing factor on top of everything else.
Start with the basics first to help keep cost down and to help judge where you are in terms of milage and we can go from there.

 

i'm not sure what "seafoam" is but i'd suggest running some fuel system cleaner through there also. do you still have a stock intake?

 

Already done pcv valve, plugs, wires, air filter.
And they induction service we have at my shop is better than Seafoam.
Its a pretty rugged chemical thats shot into the throttle body and cleans all the carbon build up out of the throttle, intake, and blows it out the exhaust.
Kinda fun to do it and smoke out the shop

 

well in that case i'd say, fuel filter and some fuel system cleaner. if ur breathin good that's the only thing i can think of. do you have a cel on?

 

sounds like maybe an o2 or cat issue. I didnt have a CEL when my cat was bad, and it failed the emmission miserably

 

I concure with all of the above.

 

i was going to say o2 sensor but the only times i've heard of it going bad they had a CEL on....