SDI Polo: Specs, Price, and Review

Hello, I have an SDI Polo. Now, regarding the problem: when I'm on the highway and give it full throttle, it accelerates relatively normally. However, if I let off the gas a bit, say around 130-140 km/h, it accelerates much more than when I'm giving it full throttle. How can that be? I also have the feeling that something is stuck somewhere. The filters are new, I had a diesel injector cleaning, and the fuel injection pump was replaced. ARG, it seems defective.

Best regards,
Jürgen F.

A possible cause is a faulty exhaust gas recirculation (EGR) valve that is not closing properly.
Does that mean that the engine is not getting enough oxygen? If so, will the engine produce soot during the process you described?