Golf TDI Shakes at Partial Load Only

Hi,

We have a very strange error here.
It's a Golf, model year 1994, with a 1Z engine.
When driving and accelerating gently, starting around 1500 RPM, the car shakes quite noticeably, and this is consistently reproducible.
When you accelerate with full throttle, it smoothly reaches 150 km/h (which was enough for testing).
If you just let it roll comfortably, nothing happens.
The best way to do it is to be in 4th or 5th gear at around 80 km/h, with the engine RPM at approximately 1600 RPM, and then accelerate with about half throttle. If you give it a little less gas, it will accelerate smoothly. If you give it a little more, nothing happens.

Today, we first checked the mass airflow sensor (MAF) using VAGCOM, and it was okay. The boost pressure also showed good values.
Then, we started the injection process using TDI Timing... the value was at the lower limit, and we thought that was it. We adjusted the pump precisely to the midpoint (blue line)... but the error was still present.

All other values are also good, and no abnormalities are apparent.

The only things that come to mind now are possibly the injectors or the fuel pump.

Has anyone ever experienced something like this before?

vagtuning wrote:

Has anyone ever experienced something like this before?

Yes, thousands of TDI drivers.
The specific circumstances may vary, but I'm willing to bet that "your" issue can already be found here through the search function, even if it's described using slightly different words.