Twin-charged engines switch between the supercharger and turbocharger to produce sufficient power throughout the rev range. They also work simultaneously. The supercharger is engaged and disengaged at low engine revs through a magnetic clutch which also interacts with the drive belt. It essentially slows the car down in order to work -and build up pressure- because it adds load to the engine through the drive belt (something like an a/c compressor). Of course, it produces more power than it consumes.
At 3,500 rpms the supercharger will disengage since it's no longer needed, which is done by the magnetic clutch. This transition should and mostly does happen smoothly. In some cases however, when for instance engine revs are lower than 3500 but the supercharger is disengaged because of low load and you suddenly put load on the engine, the supercharger will engage and disengage rapidly -when the engine hits 3500 rpms.
Because it will only be asked to operate for a brief moment, it will only slow the engine down without having enough time to build up air pressure before it disengages. Essentially the drive belt will engage the supercharger, slow down, and disengage it before it gets any of the benefits, which could be experienced as suddenly turning on and off a very big a/c compressor (like a jolt or kick). You should experience it as an acceleration burst/kick because it's followed by the turbocharger's push.
This should only happen to twincharged engines (TSI's with 140, 160 and 170hp engines, but not the 122hp or the GTI) and only around the 3500 rev range. It is also more likely to happen during a down shift or when transcending from a low load to a high load scenario while at or around 3500 rpms.
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