Control Unit Help: Troubleshooting & Repair

Hi everyone, I could use your help.
After a long illness and the resulting unemployment, I have finally found a job again. However, I now have a relatively long commute, so I had to buy a fuel-efficient car. I chose an older Passat Variant TDI (manufactured in 1994, GL trim).
Unfortunately, my current bank account didn't allow for more. It seems to be an "honest" car (second-hand, the previous owner had it for about 10 years and was almost 60, the inspection stickers are almost new and without issues, okay, it has a few dents, but what can you do...). The only problem it has is the engine control unit. However, the seller told me about this before I bought it. The unit broke down three months ago and was replaced with another, used one (I have the invoice). Understandably, the seller didn't want to invest another approximately 1000€ in an original one. Since the engine control unit is not original, the Passat has two issues. First, the engine runs a little unevenly at certain speeds (it's best described as a slight vibration, like you're trembling...). Second, when accelerating (engine speed above or around 3000 rpm, regardless of the gear), it doesn't want to go any faster. You have to maintain the speed and then you can accelerate gradually, in small increments.Currently, an engine control unit with the following number (VW/Bosch) is installed: 028 906 021 B.
0 281 001 172/173. Previously (the original part might not be correct due to the manufacturing date of 18.11.97... perhaps the first owner replaced it). The defective control unit I was aware of was 028 906 021 FC / 0 281 001 566.
I hope you can help me. Firstly, are both issues really caused by the control unit (which I assume and hope is the case)? And secondly, and most importantly: Which compatible control unit do I need for my Passat (66 kW, engine code IZ)?
Thank you in advance. I really want to avoid taking my car to the VW workshop, mainly because of its age and the exorbitant costs there.
Best regards,
Andreas

Hello.
What could possibly be wrong with the old man?
The jerking is more likely caused by a dirty flow control valve.
Best regards,
Dirk

Quantity control device, right, that's where the "jerking" comes from.

The decreasing performance above 3000 RPM suggests a pressure loss in the charge air system.

Possible causes include leaks from the turbocharger, an aging LLM (likely referring to a software or system component), a malfunctioning EGR valve that doesn't fully close, a faulty N75 valve, an NBF (likely a specific part or system), or a combination of these issues. A turbocharger defect (LDA) should also be considered and addressed.

The technical articles actually contain everything necessary to locate the defects...

I bought my 1Z 4 months ago with the same symptoms, but thanks to this forum, it's running perfectly again, except for the tendency to jerk.


Best regards, Ray.

Hello,

Your vehicle identification number (VIN) would be helpful. There are several tax authorities involved.
The part number is the same, except for the ending letters.

If you plan to use the car for a longer period, acquiring a diagnostic interface is definitely worth considering. Otherwise, you won't get very far.

First, inspect all the vacuum hoses in the engine compartment.

Here are a few tips for dealing with the quantity valve, specifically using diesel injector cleaner.
It also helped with my Golf 1Z.

Does your car smoke when you accelerate?

Hello,

So, it doesn't make any noise when accelerating.
And the identification number is: WVWZZZ3AZRE165360.

Best regards,
Andreas

Hello,

"028 906 021 FC" might be the correct part number for your car. However, since there are several part numbers for the 1Z (with FC/FF/AT endings), I'm a bit unsure how they differ.
Possibly, they are just programmed differently.

Perhaps you could send the old device in for inspection. It's possible that nothing is actually broken.