In the quest to get more MPG out of my 3.0 TDI (currently averages 33MPG - 36MPG on a long run going easy) i thought about trying an injector cleaner Anyone used one? This one is a 1 bottle per tank, to give an intensive clean: Halfords | STP Diesel Injector Cleaner 200ml or the less intensive is this one: Halfords | Millers Diesel Power Sport 4 500ml Anyone tried these? Do they do any good? The millers features a kind of "Octane Boost" as well as cleaning the injectors, but requires it almost every tank. What do you think?