What's wrong with this?

hello,
I am writing to the forum on behalf of my brother-in-law.
During the last inspection, the friendly staff at VW discovered that the mass airflow sensor (MAF sensor) in the VW T4 2.5 TDI 102 PS was defective. It was then replaced.
Since the air mass meter was replaced, the engine now has less power, and the fuel consumption has increased by about half a liter.
The complaint to VW was disappointing; the error memory was empty, and everything appeared to be fine.
Upon further inquiry as to why the performance was noticeably better before the replacement of the mass airflow sensor (MAF) than it was afterward, the response was a shrug and a reference to manufacturing tolerances.
My brother-in-law is now very , can anyone help or offer advice on how to restore the performance ?
Hi Bastianna,

The first question is how they intend to determine that, or what error they are referring to.
It will likely (unfortunately) not be possible to determine that definitively later on.
For further troubleshooting, something like diagnostic log files would be necessary.

Best regards, Rudi.

Hi Rudi, first of all, thank you for the quick reply.
We don't know exactly how or what they determined was wrong with the mass airflow sensor (MAF), because the car was running fine. However, since the replacement was done during the warranty period, it didn't matter to my brother-in-law. The warranty has now expired (it's been a few months). But he's subtly bothered by it, and whenever we drive my car (A6 AEL), he always brings up how much better his T4 used to run.
How can I create a log file? Do I need to contact someone for help?
Hi Bastianna,

bastianna wrote:

How can I create a log file? Do I need to go to the friendly

?
If you have a VAGCOM device (or know someone who does), you can do it yourself. For the basics, read the diagnostic technical article if you're not already familiar with it.