My Brother's little Daihatsu Sporttrak got worse and worse on fuel until it ended up doing 20mpg (about the same as my Rangie!) out of a little 1.6! We spent hours fiddling with the damn thing. It rolled freely, the FI system seemed to be in tip-top condition, ignition and all consumables too - temp sensors were reading properly etc. - never did work out what was wrong with it.