1998 vectra 2.0 dti black smoke?

my vectra deisel has started to puff out black smoke ,quite a lot at times .can clear it by accelerating but this sometimes causes engine management light to come on and this in turn sometimes puts car in nursery mode. by stopping and removing key and restarting i can reset everthing and start the whole process again by coincidence this also starts traffic master. fuel consumtion is still pretty good and car when not smoking still does motorway speeds ok had erg valve cleaned but no difference