No Speed Limit: Freedom and Performance

Hi everyone ,
I've looked at various articles and have to say I've gained a lot of new information. Now, I have a question, and maybe someone can help me.
I drive a Golf 4 with 81 kW, which has been tuned with an additional module from the company Wendeland. The result is very satisfactory (100 kW, 300 Nm).
'However, I'm having a problem and can't find a solution. The vehicle accelerates up to 200 km/h without any issues, reaching approximately 4100-4200 RPM. After that, it tries to accelerate further, but it's being held back, then it accelerates again. This 'jerky' behavior, as I'm calling it, only occurs at this RPM and only in the 4th and 5th gears. In the other gears (1-3), it runs all the way to the RPM limiter. This 'jerky' feeling can only be felt; there's no visible indication on the tachometer or speedometer. It's as if it's not getting enough air. Is my assumption correct that this is related to the mass airflow sensor (MAF), and if so, is there a way to test this part myself? A MAF sensor from Bosch costs 266 Euros.'
The VTG (Variable Turbine Geometry) has been made functional and checked as thoroughly as possible. The air filter is okay, and all hoses are leak-free.

Thank you for your tips.
Matte.

Hey everyone, I finally found the problem – the LMM (likely referring to a lambda sensor or lambda probe) was close to its wear limit, according to the workshop.
Since the engine is tuned, the error only appeared with the tuning box installed and was not present in its original state.
LMM replaced, and now everything is clear.

By the way, AUDI no longer uses this type of mass airflow sensor in the A3, due to too many failures.

Dull .