I finally moved from the mountains (Rockies) at 8000 ft. to almost sea level just in time for Hurricane Katrina. My car was spared, more so than my beautiful home in South Mississippi. Question, my mpg went down since I arrived to about 23 mpg hwy driving, at relatively moderate speeds. I've had problems with all my other cars/trucks making the altitude change, like the computer never really adjusts. My 03 Forester XS has 30K and had the 30K service done on it. Do I need to reset my computer by disconnecting the battery for an hour or so to "relearn" the atmosphere here? I've been here 2 months already.

I'm guessing that since the air pressure sensor is seeing more pressure then more gas is being added for the mixture. You may be stuck with what you got.

I finally moved from the mountains (Rockies) at 8000 ft. to almost sea level just in time for Hurricane Katrina. My car was spared, more so than my beautiful home in South Mississippi. Question, my mpg went down since I arrived to about 23 mpg hwy driving, at relatively moderate speeds. I've had problems with all my other cars/trucks making the altitude change, like the computer never really adjusts. My 03 Forester XS has 30K and had the 30K service done on it. Do I need to reset my computer by disconnecting the battery for an hour or so to "relearn" the atmosphere here? I've been here 2 months already.

 

I've had 2 different vehicles flip their CELs on altitude changes so I'm sure there is some effect on the 'system'. It wouldn't hurt to reset the ECU and recheck the tire pressure.