Car starts to regulate turbo pressure up and down and makes a shutter noise when accelerating slowly, about half throttle. Sounds like turbo shutter, "pfhehehehe". Theres also a hissing sound, when it doesnt do this, like air going trough a narrow opening.

No fault codes normally, but it has gone into limp mode two times at full acceleration, fault code on boost pressure too high.

It got better after I recalibrated the EGR in VCDS. It goes away completely if I disconnect EGR or throttle body, but then engine light comes on and glow lamp flashes. I have replaced both EGR and throttle body with used ones, no change.

What could cause this? What does the ECU use as input for regulating the EGR, some pressure signal?