Audi A3 Power Loss: Troubleshooting & Solutions

Hello fellow forum users,

I own an Audi A3 PD with 130 horsepower, manufactured in 2001, and I'm experiencing problems with the engine's performance. Here's a brief history of the issue:

- No issues up to 40,000 km.

- At 40,000 km, a performance upgrade was carried out by the company Wendland Tuning, increasing the power to 163 hp and torque to 380 Nm.

- After approximately 2-3 weeks and 2,000 kilometers of driving, a noticeable loss of power became apparent, which manifested as...
The car now has a top speed of only 220 km/h (approximately 240 km/h immediately after the performance upgrade).
Before the performance upgrade, it reached approximately 225 km/h, but felt very sluggish even from 180 km/h. When accelerating, the full power (the 'kick' that you feel with the stock engine around 1900 rpm) was only noticeable at 2000 rpm.
Immediately after the tuning, the full (peak) power was consistently noticeable and present from 1500 RPM up to 3500 RPM.

- After noticing this loss of power, I called Wendland-Tuning and inquired about the reason.
There could be several reasons for this loss of power. I was advised to have the mass airflow sensor checked by an Audi technician.
I had it checked, and Audi couldn't find any errors. Then I went to Wendland Tuning, and they found an entry in the engine control unit's error memory that roughly stated:
'The mass airflow sensor is faulty and needs to be replaced. Additionally, the MAF sensor was providing slightly low readings at engine speeds above 3000 RPM. After identifying this issue, I returned to Audi and inquired about their measurements. The master technician at the Audi center explained that, according to their standardized procedure for testing the MAF sensor, the values are only compared at 3000 RPM.'
Great sausage, why not install a rev limiter at 3000 RPM .
Certainly, you then also identified the problem (including the error code in the diagnostic memory) and replaced the mass airflow sensor.

- After replacing the mass airflow sensor (MAF), there was a noticeable improvement, but unfortunately, it was only a slight improvement.
In addition, after replacing the mass airflow sensor (MAF), a type of turbo lag appeared, which manifested as follows:
Constant speed, for example at 60 km/h (it didn't actually matter what RPM, gear, or km/h), then release the accelerator, then full throttle: for 2-3 seconds, absolutely nothing happened; only then did the power come on.
Now, let's move on to the curious part of the turbocharger.

- Great, the problem with the turbo lag seems to have resolved itself somehow, but now I'm experiencing a partial [issue/problem] instead.
occasional, but not always present, strong exhaust bursts during acceleration (full throttle).
In addition, my engine consumed a significant amount of motor oil, approximately 1/2 liter, over a distance of 1500 km.
Of course, I refilled the missing oil to the maximum level indicated on the dipstick, ensuring it was precise and allowing a 15-minute waiting period so that all the oil would settle in the reservoir. After a test drive of 400 km, I checked the oil level again, naturally after another 15 minutes of the engine being turned off.
Resultat: Ölstand war immer noch Milimetergenau auf Maximum. Strange?!

Okay then, this is the current status of my short history .

Does anyone know what might be causing this unusual behavior in my engine?

I am grateful for any advice you can offer.

'Does anyone have a picture showing the location of the turbocharger and the EGR valve in the engine compartment? I would like to check the vacuum hoses that lead to the membranes of the VTG (Variable Turbine Geometry) and the EGR valve.'

best regards
Alex.