thought of too much fuel going beacuase of worn fuel injectors ? for
example.

Also, you didn't mention temp sensor which is always top on the list for
running rich.
the one in the cooling system, not the one in the AFM.

this part is so inexpensive, and so likely to be a culprit
(   " a " culprit, not " the " )
that if the part is original, like 15 years old, you want a new one in
any case.

There should be another noticable symptom or two to accompany your low
fuel milage.
Dark tail pipe, darkly colored spark plugs, low power, excessive power (
rare ) etc.

if you look in a trouble shooting charge for poor fuel milage ( for all
kinds of cars ) you will also see
dragging brakes, low tires pressures , incorrect wheel alignment, etc.
How about, does the oil smell like it has gas in it ?  Any backfiring ?
rough idle ? there should be SOME other symptoms to key off of.

      scott