ESP Failure: Common Causes and Solutions

Hello,

I also have a TDI engine with the code AGR, in an Octavia, since the end of January.
Right from the moment I bought it, I noticed that the engine didn't run very smoothly at idle. It was shaking irregularly.
During the drive from Solingen to Munich, I noticed that it was producing quite a lot of smoke.
During the continuous testing, it was also noted that the vehicle consistently consumed 2 to 2.5 liters more fuel than what was indicated by the Multifunction Display (MFA).
Within 3 months, the shaking became progressively worse, causing the entire car to vibrate. Even while driving, it was noticeable in the lower RPM range that the engine wasn't running smoothly. Furthermore, black smoke started to appear as early as 1500 RPM.

At my main workshop in Dresden, it was discovered that the tensioner pulley for the timing belt had seized, and the timing belt had too much slack. It was replaced along with the tensioner and all the idler pulleys.
The stuttering was gone...

But it only reappeared after about 500 km. Then it was back, and it became much more intense in a significantly shorter amount of time.
Interestingly, there was never any loss of power. With its 90 horsepower, it easily reached speeds of 190-200 km/h according to the speedometer...

One day, the engine simply stopped working while driving on the highway at 190 km/h, and it wouldn't start again.

At a Skoda workshop, it took 3 hours to figure out what the problem was. A motor fuse kept blowing, which prevented the engine control unit from being read.
After the fuel injection pump was disconnected, the fuse no longer blew.
The workshop said that there was an electrical fault in the fuel injection pump, specifically a short circuit at the fuel switch.
The pump was replaced, and now, suddenly, my mass airflow sensor is broken????

Now, my actual question is...

Could the excessive black smoke and increased fuel consumption be due to an electrical fault in the ESP (Electronic Stability Program), or was it more likely a mechanical issue, and in my case, are both problems occurring simultaneously?
The engine has only 160,000 kilometers on it.

I'm curious to know how this defect occurred, because the private seller claimed that the car was in perfect working order. That clearly wasn't the case, but how did he manage to damage the ESP system so badly?

Thank you for your help.

Regards,
Alex.