306 hdi power cut out problems?

hi i have a 306 hdi d turbo 2000 that i have just bought that i have a slight problem with. when you accelerate hard the car will cut out. the engine managment light is on all the time. although if you feather the throttle it seems fine i cant work it out. i have changed the fuel pump in the tank as i had a spare and the fuel filter but makes no difference. if anyone has any ideas it would be muchly appreciated.