The boost pressure fluctuates (somewhat rapidly) in my 1994 850 Turbo.

I’ve posted this question on another board and had little luck. A co-worker informed me that the individuals on this board are very knowledgeable and sometimes provide better and or more input. Here’s hoping. :)

If I pin the throttle, it will build full boost, however, as soon as it reaches full boost, it drops to near atmospheric. From there, it continues to build to full boost and then drops off again (this time not quite to atmospheric, each drop off is less than the preceding one).

This process continues through redline and is not in sync with gear changes.
It has been suggested that this might simply be a leak. I've looked around and not found anything; I have sprayed carb cleaner around all the connections and observe no change in engine speed.

I can't imagine how a simple leak in the system could cause this. I've had leaks before and they simply resulted in not building full boost, or taking a long time to do so. This is a pretty rapid fluctuation, say between 1 cycle a second (1 Hz) and 1 cycle every two seconds ½ Hz.

Is there a way to check the bypass valve and the waste-gate?

Any help would be much appreciated.