Sounds like tired diesel injectors. But really you need to get the car checked by a competent garage before spending a lot on injectors. They can be removed and tested, re conditioned and or replaced, your choice.

You can try a few tankfuls of Shell V Power before you go down this route. A few miles wont make a difference you will need to drive some hundreds of miles for Shell V Power to do its work but if the injectors are tired/ faulty then this wont make much difference.

My 60 year old Mercedes diesel runs great with no smoke but I had to get the injectors cleaned and re calibrated, but they are now good for a further 20 years or more.