AH!!! My bad!
I never even considered it being a diesel!
In that case it will be due to a severe carbon build up within the intake manifold. This may be a bit more involved though due to this engine and it's design.
Be sure to buy your diesel somewhere good - cheap fuel causes huge build ups and can damage your common rail injectors quickly!! Always try to use Shell or BP where possible - NEVER any supermarket or Spot fuels ect!
You are gonna have to have inlet tract off and physically remove all the build up I would say with those faults.
Apologies again for assuming your motor was petrol! I should have read up as on many earlier posts you are pretty clear!!
