It has been an endemic issue since the PQ34 platform came out in 1998 and has carried on through PQ35 and 46 into MQB and is down to the side engine...
Failure of the vacuum pump is possible but you would expect some engine EGR and turbo fault codes in the engine as they use the same vacuum source so...
The ECU has very accurate engine position and speed sensing so in conjunction with it seeing raised emissions via the two lambda sensors, it can tell...