e46 325ci m sport runnin rough

[arifvw]

hi peeps,ive only had my bimmer for about 5 weeks and last ngt when i started the car,and the cat lgt came on and the tick over was very lumpy(felt like it wasent firing on all s1x cylinders).got it diagnosed this morning and it came up as a fault with coil pak no 4.swapped that round with my mates,and no joy.......anybody got any pointers on what it might be....me and my mate are going to av a look at the injectors.....any body experienced a similar prob to this?