engine malfuntion

hi all i have a ford C Max 1.8 diesel 2008 with 48000 miles on the clock ,im driving along when the engine malufution light and the chime come the engine goes very lumpy if i turn off the engine for a few second and then swith back on the engine is still lumpy but if i rev it to 4000 revs a couple of time it clears and i can then continue on my way anyone got any ideas to what the problem may be ,i have already changed t fuel filter as i was told this could help

chuckfred