@R055IE

As you got a solid primer bulb "Pump it at idle" several times to purge a bit.

As Bill @BillsGU, suggested clean you boost controller (Tillix/Dawes).

Try your testing with you needle valve fully closed, CRD can handle max spool.

If still no joy we can isolate manual boost control and run actuator direct off vac line. Hold off on this at this stage, need to very careful not to overboost.

What boost gauge U have and what is the max scale reading?
What max boost or bounce are you getting with quick full pedal with slight eng load (say 40-50%)?

Out of interest, have U blocked your EGR?