RS 6 shifting problem GAG

Hello everyone,

I'm having a problem with an RS6 B5, transmission code GAG, ZF 6-speed, manufactured in 2004. Under full load, the automatic transmission doesn't shift gears 1 and 2 smoothly. There's a loss of power followed by a strong jolt when engaging second gear. During this process, I notice that the engine speed fluctuates from 6200 RPM to 5500 RPM. This occurs in D, S, or Tiptronic mode. Under normal driving conditions, everything seems fine; all gears shift smoothly.
What has already been done: Due to a failure in the input shaft, the transmission was completely overhauled 6,000 km ago, including the torque converter.

"As a test, two lambda sensors from eBay were installed. Now, the automatic system switches without any problems... However, these lambda sensors are providing incorrect values to the engine control unit, causing the check engine light to illuminate. The engine is running far too rich; in partial load conditions, the lambda control value measurement block 32 shows -25% (on both bank 1 and bank 2)."
Furthermore, the wiring between the mass airflow sensor (MAF) and the engine control unit (ECU) was checked for resistance levels.
The lambda control was deactivated as a default setting, and the switching process is not improved.
Has anyone else experienced this problem or have any suggestions for a solution? I would appreciate any input. Best regards, Dani.

Please use decent LLMs, as it is well known that scrap from eBay almost always causes problems.

Currently, new original lambda sensors (oxygen sensors) have been installed. The issue is that when the engine runs rich (too much fuel), the gear changes are still working correctly, which, in my opinion, rules out a problem with the automatic transmission.

Servus Mille!

If the LMM (likely referring to a Lambda Measuring Module or similar) is truly faulty and new, I would next check all temperature sensors on the engine and transmission to ensure they are reading plausible values.
So, it completely cooled down overnight and then returned to its operating temperature, possibly with logging enabled to identify any interruptions or anomalies.

If an incorrect but still possible value is transmitted to the respective system component, no error message will be generated, but this can lead to an incorrect calculation of the applied torque, which may result in the observed behavior.

Best regards from Munich!

EDIT: I'm assuming the correct oil level in the transmission is already established, right?

Thank you for your reply. The temperature sensors have been checked multiple times for plausibility, but unfortunately, they are all working correctly. I took a closer look at the engine control unit and opened it. I found a Japanese chip from NEC inside the Bosch ECU (see photo). Now I suspect that the RS 6 has been tuned, but I cannot confirm this with 100% certainty. Has anyone else here opened such an engine control unit? Unfortunately, Google is also not providing any information about the chip. I think I will first try using a different engine control unit, as I am unsure whether the data processing in the tuned ECU is reliable.

The chip you found is a 128k SRAM.
Full designation: uPD043100AGW-80Y.
It has absolutely nothing to do with tuning.
It is perfectly normal for an engine control unit (ECU) manufacturer to use electronic...
Components are used that are available on the global market.
At SRAM, NEC was one of the few manufacturers.

Best regards,
Micha