OK, thanks Mike. I'll get the catalyst changed to see if that fixes the problem. If it doesn't, do you have any other ideas of what to investigate next?
OK, thanks for these ideas. The fuel pressure may well be worth checking if the catalyst change does not work. However the Sharan does not have a throttle body - it uses unit injectors - I suppose that the nozzle tips on these may have become partially blocked with carbon deposits over time, but I think that servicing unit injectors is a major job - my VW main dealer wanted £2K for a new set!