2001 Mercedes 311 CDI sprinter?

About once a fortnight or after about 500 miles the EDC light on my sprinter will come on, it will lose power, then after a few minutes cut out. After a minute or two it will restart, the EDC light goes off and it will run O.K. for a few weeks, before happening again. I have changed the fuel filter as stated in the hand book but the problem still persists. Has anybody experienced this problem as well and how can I rectify it?
Thank you and regards.

Mick
June 2009