AFN Wave Acceleration: 1800-2000 RPM

Hello,

"For the past few weeks, I've been experiencing a wavy acceleration in the AFN (likely referring to a specific engine parameter or system) between 1800-2000 rpm. Strangely, everything seems to be fine before and after that range. The maximum speed is also reached relatively quickly."

Regarding the vehicle: Audi A4 Avant, manufactured in 1999, with a faulty AFN AGR valve, approximately 115,000 kilometers.

I've already read technical articles about the LMM (mass airflow sensor), but I don't think that's the problem, as it was replaced about 40,000 km ago. Given that it's happening in the 1800-2000 rpm range, I suspect it's related to the turbocharger or the variable turbine geometry (VTG) adjustment. What's also strange is that the car makes a bit of a humming noise in that rpm range. The humming was already there before, but it didn't bother me much.

I've already read the error codes, but unfortunately, I haven't found anything.
Is there any other diagnostic trouble code (DTC) data I can log to help me track down the problem?

Regards,

Thomas.

thom wrote:

I've already read technical articles about the LMM, but I don't think that's the one; it was already replaced about 40,000 km ago.

Hi,

There is also a separate expert opinion regarding the wave-like acceleration .

Quote:

Are there any other MWB (measurement data) I can log to help me track down the error?

Start with 8 + 11...

Today I took out the mass airflow sensor (MAF), but it looked good and wasn't dirty at all. What was strange was that the MAF sensor, which should have been replaced around 75,000 km, wasn't from Bosch, but from Pierburg. Also, the MAF sensor connector only had 4 pins.
After that, I checked the VTG strut and started the engine. It behaved as described in the technical manual, and it responded well to short bursts of throttle. However, the strut didn't move when the engine was running at a constant speed of 1800-2000 rpm.
Tomorrow, I'm going to log the data from the two MWB devices.

I logged two "MWB" today.
Unfortunately, I'm not very familiar with Excel, otherwise I would have created a chart.
I also know that the number display doesn't look very good.
During the test drive, I accelerated from a standstill (0 km/h) and shifted through all the gears until I reached approximately 100-120 km/h in 5th gear.

- Diode trick
Or just try a new one. That's what I did with my AFN.