UKPassats

I have recently changed my glow plugs because the car ran really rough when cold. Its much better but still has a misfire and white smoke when started until its warmed up, but even then when sat at idle there is still sometimes a misfire. It also feels like it loses power sometimes.
There is also a loud taping noise coming from the engine, i think its coming from the tandem pump but not sure if it's injectors, my mates just say its a diesel noise but im not convinced

Anyone any ideas???

Thanks