2.0 TDI BKD engine, 100,000 km, experiencing misfires and loss of boost

Hello fellow DIY enthusiasts,

I'm having trouble with the BKD engine again.
To begin with, this vehicle does not have any coolant leaks, and the intake manifold flap (V157) is new.
The car jerks when accelerating, starting from 2nd gear. Speed from approximately 2000 RPM.
So, I plugged in VCDS and, lo and behold.
The following information is stored in the error memory:

17058 - Spark plug, cylinder 4 (Q13)
P0674 - 000 - Electrical circuit fault.
Environmental conditions:
Speed: 1029 RPM
Torque: 122.0 Nm
Speed: 0.0 km/h
Last: 0.0%
Voltage: 11.10 V
Binary value: 00101111
Temperature: 4.5°C
Binary value: 01110000

This spark plug will be replaced immediately, but I don't think this is the reason for the engine misfire.
Okay, so the usual suspects: Log entries 3, 8, and 11.
This indicated that the boost pressure in the upper range (from approximately 3500 RPM) was 200 mBar too low (see log file). As far as I understand, the AGR (Arbeitsgemeinschaft für relevante Informationen) is also incorrect.
Since I'm not a professional, is my assessment correct, or what's the opinion of the professionals?
I also logged the LMM, and it seems to be working correctly.
Next, I will check the intercooler pipes to see if there are any leaks.
What would you guess? Turbocharger (Variable Geometry Turbine), EGR valve?

I'm not entirely happy with the LOGs, as I did this on the snow-covered road.

"Thank you very much!"

Sure, here's the translation:

"SG Servusssss"

Hello,

The boost pressure is generally relatively low before it drops. Is your vacuum system okay, and is there perhaps a vacuum hose that has been chewed through or a membrane that has been torn (e.g., the VTG adjustment on the turbocharger, swirl flaps, etc.)?

Best regards, Rainer.

Hello,

First of all, thank you for the response!
I replaced all the glow plugs, so the error memory is now clear.
The stuttering/jerking/shaking hadn't gone away.
Okay, I've checked the entire intercooler piping system, and I haven't found anything.
Then I checked the vacuum hoses, and lo and behold, one of the clips on the vacuum distributor (or whatever that thing is called) wasn't attached.
The stuttering is gone now, but I still created another log file.
The data looks normal to me, so the problem should be resolved.

Sure, here's the translation:

"Best regards," or "Sincerely,"

P.S.: I had to do the logging on snow, so it wasn't ideal.

Hello,

Yes, the logs are suboptimal because there's not much full throttle. But it looks much better.

Thank you for the feedback!

Best regards, Rainer.

As an addition, because the spark plug error initially misled me.

The case of the 16V PD TDI engine being discussed here is something entirely different from that.

"8V PD TDIs are known to have a specific type of problem."
1 error found: [code]
005660 - Spark plug, cylinder 3 (Q12)
P161C - 000 - Interruption.
Environmental conditions:
Error status: 01110000
Error priority: 3
Error frequency: 1
Mileage: 138,712 km
Time: 0
Date: 2000.00.00
Time: 11:52:44

Environmental conditions:
Speed: 945 RPM
Speed: 0.0 km/h
Last: 3.1%
Voltage: 14.52 V
Binary value: 00101100
Temperature: 6.3°C
Binary value: 10110000

Here, the power rail broke.
It's located on the outside, along the head, just like it always has been on the 8V models.
Interestingly, it's ALWAYS the Q12 – now the third one in a row that I've randomly logged.

Perhaps the contact clip breaks because people are hitting it in the wrong place when changing the oil filter.

There's no noticeable shaking, and of course, replacing the crankshaft pulley won't fix the problem.

The solution is to replace the power supply's "antenna."

m;