Renault Trafic 2008 2.0 diesel rough running?

The problem started 2 days ago with a slight hesitancy when accelerating hard in 3rd gear. yesterday the hesitancy was worse now in 2nd and 3rd gears. Today it is now running quite rough with no power, won't rev over possibly 2000 revs dies when trying to accelerate but will run on a light throttle but no real power. when it does temporarily die the engine light and stop light come on on the dash but go out when the engine recovers. At idle it is also rough now. Can anybody point me in the right direction without reverting to the mechanics who do it by trial and error at my expense. Van has done 84,000 and has run perfect till now.