Volvo 850 TDI Start problems

Hello guys, I just signed up, maybe you can give me advice on my Volvo 850 Tdi. Year 96, 326 000 km, 170 000 driven by me, runs great, needs an average of about 6.4 liters of diesel and I have never had to pour oil apart from the oil changes. What worries me besides the strong soot development (when giving gas on the highway really embarrassing) starting at low temperatures. If it hadn’t been so warm in winter it would surely have been Probl But I also have to wear it for quite a long time and when it starts, a huge, stinking, white smoke cloud comes out of the exhaust. Since I bought the car five years ago, it has never jumped very well but that has deteriorated significantly lately. My question: Can the situation be improved without much effort or should I look around so slowly for a new car? Thank you and greeting CarlMichael