Yup sounding more like a wastegate issue. Next step is yank the pressure line on the wastegate and go for drive to test the soft spring idea.

Like I say, my turbine is not easy to spin by finger tip pressure. It certainly does not 'freewheel' when spun. You have to push it around in circles and when you stop it stops. And it seems there are "stiffer" spots when pushing it around. No matter, I still get 1 bar pressure boost out of this thing with the manual boost controller.

I think the boost controller actually compensates for both issues: stiffer rotation and soft spring, by keeping more exhaust pressure on the turbine longer before wasting any.

You didn't mention if you have the ALDA on the car or not. I nearly yanked my turbo once thinking it was a culprit when instead a failing ALDA was causing driveability issues with power. To make the long story short, yank your ALDA off while you are diagnosing power issues before zeroing in on what you think is a turbo issue here.

I know it's tight for space on this car to remove ALDA completely but you can just unscrew the big nut and allow ALDA to ride up so it is just resting / wobbling on top of the IP. That's good enough to experiment. From the front of the car, you can get a long handled big flathead screwdriver blade on the square part of the ALDA and just whack the end of the screwdriver to rotate the ALDA... you may or may not need to hold the big nut with a 27mm open end wrench when you do this. The screwdriver alone was enough to crack the threads of the nut, then I was able to spin the nut by hand.

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Cheers!
Scott McPhee

1987 300D