Boost Pressure Too High Audi A4 8E 2.0 TDI

Hello everyone!!
I'm writing to you now because I'm starting to get really frustrated with my father's Audi!


The vehicle is an Audi A4 8E 2.0 TDI with 103 kW and DPF, with 256,000 km on the odometer, and is experiencing the following problems:

At an engine speed of approximately 1700 RPM, the engine starts to sputter significantly, and the turbocharger makes very loud hissing and air noises.
Finally, the preheating indicator light starts to blink.
Error code read: Turbocharger pressure exceeded!! Should be 2.2 bar / Is 2.6 bar!!
After that, I checked the diesel particulate filter and found that it is 96% clogged.
So, I tried to get out of it by using chemical cleaning and a forced regeneration.
After approximately 30 minutes of driving at around 2000 RPM, everything burned off, and there was still 8% charge remaining.

Then the car ran normally for about 10 days without any problems!
Suddenly, the sputtering and the noises coming from the turbo started again...

I thought the DPF was probably clogged again, so I immediately ordered a new one!
Unfortunately, it's not an original Audi part, but a replica costing €250.
Installed it immediately after delivery, but the problem is still the same!!

I've already replaced several parts, and I'm at a loss for what to do next.
New poetry.
Turbo, new.
Boost control valve, new.
Pd elements installed new seals.
NW and Stössel are new.
AGR valve cleaned and inspected.
"I checked the throttle valve and found that it's only opening to 25%. This is likely causing the noises from the turbocharger, and it's also causing the boost pressure to be too high, as I suspect it's being restricted by the throttle valve."

I've been working in the automotive industry for 20 years myself, and I hope you can help me with this.
Thank you in advance for your help!!

The classic, with endless automotive experience, and what does he do... he trades everything .

I work in a completely different field, but I'd like to try and help out.

"A new DPF for €250 seems no better to me than a full, original part."
2. Chemical cleaning - loading...? So, let's first address the ash mass in the filter. At 250,000 km, it might be at its maximum fill level. A simple search here in the forum will reveal many tricks to save money. You can clean this thing... here's a small tip.
3. Parts Replacement Spree: Why were the Turbocharger, Power Distribution (PD) elements, Nozzle Washers (NW), and control valves replaced? Was there simply too much money available, or was there a strong desire to tinker? What were the indicators that led to this?

Here's another tip: It seems you have access to diagnostic equipment. Therefore, perform an auto-scan according to the forum rules. Then, log the relevant parameters and show them to us.

After that, please arrange your story chronologically so that we know what happened to the cart.
As an uninformed reader, I assume that because of the high boost pressure, you replaced everything, and you still have too much boost pressure... Or, you replaced the turbocharger, and now you have too much boost pressure. Please explain to us, in simple sentences without flowery language, what happened, when, and in what order, and then we can proceed.