Hi I have a 1999 R170 that shows up two fault codes, P0170 Fuel trim bank 1 and P0303 cylinder three misfire. I swapped no. 3 plug with no. 1 but still got the same result. The strange thing is the car runs and idles quite smoothly with no sign of a misfire. Can anyone suggest where to look next and what the P0170 code means?