Rough running - fault code explaination please?

[L33 4.6]

Hi,
The X5 (2003 4.4) has develped a slight fault whereby at a steady speed the car "hiccups" and judders slightly now and again. The engine management light flickers and sometimes goes out and sometimes stays on.
It does feel like a coil pack breaking down, although my only experience of this is coil packs breaking down under heavy load - not keeping at steady speeds.

I have had the fault code read and it states "Too rich bank 2".

Can anyone tell me what a likely fix would be please? I guess too much petrol is coming through to bank 2 or something is causing the fuel not to burn efficiently and a sensor is picking up I have unburnt fuel passing it and flags up a fault.

Either that or a sensor somewhere else in the engine compartment is playing up and asking the fuel pump for too much fuel...

Its not all the time and worse when the engine is cold.

Cheers,