TDI Engine Problems: 1.2L 3-Cylinder Runs Rough

It's about a 1.2 TDI engine in an Audi A2, and it's running very roughly.
I've compared it to the identical 1.2 TDI engine in the Lupo.
It runs much smoother.

The engine is not running smoothly, and the car is vibrating a lot.

Performance is present... where should I start looking?

First, use VCDS to check the idle speed control in the measurement blocks of the engine control unit. Then, further investigate the cylinder that exhibits the corresponding anomaly.

Hello!

It was due to a PD element. I replaced all the PD elements and was able to use used ones.

They might be a bit older and look a little different, but they work perfectly fine.