So Mike says:
>         OK, so Im supposed to leave this coming saturday for Tofino, BC, so
> I sent the Mystery Machine (my 83's name) to the shop just for one problem
> that I could not diagnose. The problem was that my fuel mileage had gone
> horribly screwy after a short trip to the Hinton area one weekend. Mileage
> was ok getting there but coming home it was atroctious, as I posted in a
> previous message.

Here's my $.02 of Possibilities:
(This assumes that a full tune-up has been done)

Old battery that needs replacing
Check the main battery ground and make damn sure that
it is in good shape and has good solid metal to metal
connections.
Bad O2 sensor (or the wiring inbetween)
Bad temperature sensor (or the wiring inbetween)
Bad gas
Sticking fuel injectors.  (pour in some liquid miracle like STP fuel
			   injector treatment or the like)

Get some good gas in there like Chevron Supreme.

Make sure that all of your F.I. wiring is in good shape and has good
connections.
Clean up the throttle valve plate
Clean the throttle valve control internal contacts.

That's all I can think of for now.....

Steven 
Sacramento, CA
sjohnson@pcocd2.intel.com