This is sorta van related so hold with me.

Due to snarky drivability problems with my dear '86 Toyota Camry
(238,000 miles) I replaced my ECU coolant temp sensor.  Problem cured.
*AND* my mileage has jumped from my highest ever reading of 38 mpg
all the way to 50.7 mpg!!!

Now wait before flaming me to death.  First, this was not a case of 
'air bubble on fill-up' as the fuel gauge hardly moved on my 190 mile 
jaunt that I just checked it on.  Secondly, this was absolutely ideal
conditions:  cool air, engine warmed when filled at start of trip, 
straight highway driving (5 engine off stops for work).  Thirdly, 
speed held at not over 60 mph (recent ticket, ya know).

This feat has yet to be repeated but i wanted to share the 
preliminary incredulation with y'all.  If this was a one-time fluke 
(or error) I'll fess up to everyone (yeah, right).

The sensor on my van is going to be replaced just for the heck of it!

-dan (still amazed and not quite believing)