Audi A4/B5: Wrong ECU? Expert Advice.

Hello everyone.

I have an Audi A4, model B5 Quattro, with an AFB engine (V6-TDi), first registered on December 3, 1998, so it's technically a 1999 model but predates the facelift (VIN <X200>X048xxx, but it has a control unit with the part number 8D0 907 401 B installed.
According to the parts catalog, the control unit should have the part number 8D0 907 401 D (VIN > X030.000).

Does anyone happen to know what the differences are between the control units, and whether it might have something to do with the vibrations?

I'm at a loss for what to do, and my mechanic is too, but I can't just accept that the problem can't be fixed. A replacement control unit has already been installed, but it was an older version with the suffix 'B.'

Thank you very much.

Stefan.

Hello Stefan,

Currently, the version number for your control unit is "F".
Have you ever checked the camshafts for excessive wear? In the past, camshafts were sometimes installed that were too soft, and extreme wear on these camshafts could alter the valve timing.

From what mileage did the shaking/jerking start occurring?
Is there anything stored in the error memory?
Is the performance normal?
Is the engine and transmission mounting in good condition, or has it been checked before?
Do you have any measurement data about the jerk range?

Hello Michael,

Thank you very much for your answer.

Okay, so:
The vibrations started appearing around 90,000 km; that was almost exactly a year ago, and I had the car for about 5 months at that time (it was a used car).
After the previously described measures had not yielded any results, the 'Friendly' team replaced EVERYTHING inside the engine compartment.
Engine, transmission, fuel injection pump (2x), fuel injectors, engine mounts, power steering pump, water pump, etc. Even the driveshaft and propeller shaft were replaced, although the rear differential and turbocharger were not.

Therefore, I assume that the new engine is up-to-date, so the problem with the camshafts should not occur.

Genützt hat es... NOTHING.

The control unit was temporarily replaced as described, but this also did not yield any positive results.

'Wheels, brake discs, and similar components, such as the well-known issue with the 4-Motion system where the driveshaft is twisted, which can cause vibrations at 140 km/h, are also ruled out because the entire front brake system is brand new (312mm discs), and the rear brakes have new original discs. The problem occurs with both winter tires (brand new 16' steel rims with 205/55/16 tires) and brand new summer tires (Bolero rims with 225/45/17 tires).'

I don't know what to do next.

Measurements were also taken multiple times, but (according to Audi), no discernible errors were detected.
An injector nozzle (cylinder 3) was replaced a second time because it exhibited slight deviations from its specifications, but these were still within the acceptable range.

There's still one problem: in the semi-warm state (shortly after a cold start, after about 500 meters of driving), the engine stutters, and the RPM fluctuates between idle and just over 900 RPM. I believe this is due to a faulty temperature sensor, but the engine control unit (ECU) doesn't detect the defect (I've already tested everything).

Okay, so much text. Maybe someone else in this forum has a different solution to the problem? It seems I'm not the only one facing this issue, as someone else mentioned in the post above that they are experiencing the same problems with the AKN.

Thank you for your effort.

Stefan.