Hi Max
I also have an 2000 V6 S-Type and done 60K and had the same problem. I have changed the plugs, and coils, one of the plugs had a crack in the insulator and thought that would be the cause but after a few miles the problem started again and this time found that the rubber ends of the plastic pipes were loose and leaking air so replaced the ends and used cable ties to get a good seal and so far ok.