Hello.
Okay, I have some good news for those who are interested. The error(s) have been found and fixed.
Regarding the errors:
I reinstalled the fuel injector. And I noticed that when the throttle was open in the engine compartment, air bubbles would collect in the fuel line. The diesel pump had to process these bubbles first, which caused the acceleration lag. Then, I checked the pressure of the turbocharger and had to increase the pressure from the initial 300 hpa to the prescribed 750 hpa. I then took it for a test drive, and sure enough, the car runs great!!!
I've thought about it again and came to the conclusion that I should drive behind my car to see if it was really a blue cloud or a gray cloud. So, I did it. I sent my wife in the car and I followed her on my motorcycle. And what did I see? It was a gray cloud, and that can only be due to the fuel. Then, back home, I thought again about why it always looked blue, and I came to the solution: I have factory-tinted windows from 'Werka' that are blue!!!
'I was so silly; I could have figured that out earlier. Yes, the main thing is that the error has been fixed!'
At this point, I would like to thank you again for the numerous tips.
Thank you, and best regards, Mark from Kiel.