This is an interesting detailed thread where I am trying to troubleshoot an intermittent boost problem I have had for a while.
Whilst cruising at a constant speed for a while for example on motorway without using 2nd turbo and then I floor the throttle, the revs climbs up past 5k before the 2nd turbo decides to engage very gradually. If I back off the throttle and then repeat this again, the 2nd turbo comes on earlier as should. Seems issue is intermittent but frustrating when 2nd turbo does not engage when needed and revs climbs.
Can this be VSV associated? I tested the IACV and EGBV ones which both click with 12v power applied