I've been strugling to figure out my fuel mileage woes. And a idle that
shoots up to 3000rpm at stop lights Here is what I've had done thus far....

Mechanic #1   Checked for vacuum leaks and found that the rubber boot from
the AFM to throttle housing was cracked
                        I replaced it along with the fuel filter.......cost
$200CDN total.......result 10mpg

Mechanic #2 (VW dealer 1000km from where I live)  Engine started misfiring,
hesitating, and struggling to climb every hill it
went up...........I disconnected 02 sensor and it ran smooth but mileage was
crap
                        Took it to VW and they said the wiring to my fuel
injectors was corroded as was the grounds etc...
                        they also said my Temp II was shot (it was new in
February so it was waranty) as was my O2 sensor so it
was also replaced. This all seemed legit to me   cost $490......result
12mpg, the van did run well and idled fine
                        but the fuel mileage is f'ed and there still is a
heavy exhaust smell

ANY IDEAS WHAT I SHOULD DO NEXT

Chad 85GL van