Unround run and high consumption in urban transport

Hello dear Volvo community, unfortunately my Volvo V50 2.0d from the year 2004 brings me back to the palm with 279,000 km. On the highway great consumption values and super round engine run. Also easily creates the 200 km/h and the fuel consumption at 120 km/h is about 5.5 liters. However in the city traffic (even with activated cruise control) at 50 km/h consumption. Onboard computer beyond 20 liters. When accelerating even part 99,9 l. But on average it shows always beyond the 20 Lit I have already tried a lot and the fault memory does not emit anything (is therefore empty). – DPF changed at 230,000 km – pressure converter solenoid valve (brown part) – suction bridge cleaned – additive DPF filled up and memory resett – EGR valve new I am sure that it takes place in this phase the regeneration of the DPF. But about 400 km at a time? Then it runs again a few km (about 50-100 km) quite normal and does not jerk and then this phenomenon stops again. I want to go back to the workshop, I prefer to put my own hand in the mileage performance. The workshops think that you should get a new car. But I don’t want to accept this and hope for your help! Thank you in advance.