I once went to a bosch specialist as i had dodgey injectors, he almost cried when i said i used fuel additives to try and clear it it. He also said not to use cheap supermarket fuel?
Bottem line is dont use fuel additives, if its running funny its usually something injector cleaner isnt going to sort out. Dont these injectors run at like 30000 psi or something rediculously high? pretty sure they would clean themselves, although apparently the injector cleaner sticks to the tip like a wax and burns the dirt off, im sure the pressure would clean it off itself though....