Sounds like it's going lean coming down to idle and the ECU is struggling to 'catch' it, so stalls or over compensates (over revving).
Need to log the MAF and lambda regulator channels in VCDS and see what numbers you get as the revs fall to idle. MAF is usually around 3-4gs with the stock airbox and lambda activity should be small. If it jumps up a large amount 15% or more, it's defo lean, or the MAF scaling isn't right.
Bung the factory airbox on for a test, to see if the problem goes away?
What would cause it to go lean? Only reason why I think mine is something to do with the throttle, is because sometimes on part throttle at motorway speeds it feels like its fluctuating/jerking
Usually the MAF scaling on intake kits, but if it's not that, it will just be a good old fashioned air leak.
Mine's like that as well, at very small throttle inputs......sat behind someone doing 65-70 and coming on/off the throttle for example. It's also like that lower speeds in the lower gears, say 3rd, it's hard to maintain a constant speed.
Mine's only been like that since remapped with a linear pedal map. I bet if I was to get that put back to the factory non-linear pedal map, it would smooth all that out. I still need to get that done at some point, or bin it off and just go back to Revo. That map was smooth everywhere.
A bad throttle would fault code. I thought the same as you bought a brand new throttle from VW, revision Q, and it made zero difference.