I used to have a W123 240D which has essentially the same engine and it was virtually smoke-free, even at full throttle. I think the main thing is to have the valves adjusted properly and of course the injectors must be spraying right as well. Try an injector cleaner & cetane booster and if you have no record of the valves being adjusted, do it ASAP.

__________________
2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL