i asked this question, i found i cant really trust them,they come far and in between,i was recommended one chip used on a modded forester,(and for the life of me i cant remember what it was) but i do remember it was mixed reviews, it connected to a obd2 port, so i dont under stand it all so well...
all i can think of is ask someone with a performance shop that does ecu tunning,maybe they know something...
stay away from those "chips" or any other gimmicky crap said to improve mileage. the chips trick your car into thinking its getting colder air and hurting the car in the long run. the fuel saving devices dont work. changing your driving habits is about all thats going to help
Subaru employs hundreds of highly talented engineers, and
pays them (the medium bucks) to squeeze as many mpg as
possible out of every car they make. (Well, as many mpg
as possible consistent with a good reputation for reliability,
and low warranty expenses.)
Why would anyone trust an aftermarket hack to "improve"
economy (without screwing-up something else)?