This winter I have seen a mileage drop from 21-23 city to 17-19 and 28-29 hiway to 23-24. This is an o6 forester xt with 35,000 miles . Air filter is clean, use Pennzoil platinum and drive sensibly staying off the turbo as much as possible. The plugs have not been changed. Could ethanol be the problem? I live in Utah but the cold weather never affected the mileage until now. I`m wondering if the maap sensor or oxygen sensor should be checked. Any ideas?...Thanks:confused:

iam in the same boat, but 170,000mi legacy a/t wagon i have changed everything , except rear 02 sensor, still getting 1 code map sensor, which could affect mpg, i am only getting 20 city ,