My son is driving his '84 Vanagon with a newly installed 2.5 Subaru engine
in it back from Colorado to Ohio.  He has noticed a decrease in fuel
mileage as he comes east.  He says it runs great and accelerates normally
but he is concerned about the mileage drop, from 22 to 16mpg so far.
Sounds like a sensor problem but I know nothing about Subarus.  Anyone have
any suggestions?

Tom