Opel Combo without strength

Good afternoon,
I have an Opel Combo 1.3 CDTI, which I bought used a few months ago. When it's running at around 2000 rpm, it seems to stall, and when I press the accelerator, it's slow to respond. I've taken it to the mechanic, but they haven't found the problem, even after connecting it to the diagnostic machine; no fault codes appear. I honestly don't know what else to do to find the problem.
Does anyone have any idea what the problem might be?

Thanks in advance.

Hey friend, suggest to your mechanic that he check the diesel injection pump and the injectors to see if they're properly calibrated. Also, as a suggestion, have him check the pump itself or take it to a test bench to have it calibrated and its timing verified.

Check the EGR valve; you can disable it with a sheet of iron.

What's the mileage? Does it run rough at low speeds? Could the exhaust be clogged?

The EGR does not eliminate it in case such changing, check the turbo to see if the West Gate opens the filters as they are that time they have if it is intercooler would have to check the same.