1999 pathfinder with OBD codes 300, and 325, mult. miss and knock sensor. 3.3 4X4 I have tried at least three different fuel inj. cleaners. with some minor improvment. The car seams to have lost power. From stop the care accelerates very slowly. I still can get to full highway speeds. Idle seems to get worse the hotter the engine gets. SES light has gone on and off for last couple of tank fulls of gas. Also seems that I should be getting better gas mileage. I just changed the water pump if I have overtightend the belts could this be the root of any of these problems.