The first test you can do is to unplug it and see if the car runs better. This forces the ecu to trip to a default value.
Another test you can do requires a VAGcom
Enter Engine measuring block 003
Start Logging data
In a high gear (4th/5th), give full throttle from 2500 rpm up to 3500rpm.
Open the Log file
Graph MAF actual -vs- rpm in Excel
The MAF is OK if the actual value is at least 850-900 mg/h at 3000 rpm. if the power drops past 3000 rpm and the maf reading drops then it's usually an indicator that the maf is bad. Of course, you need a clean intake, air filter, etc., otherwise these also cause restricitons.