85 5KCST Boost problems intensify

["David C. Kowalski" <DataGenics@worldnet.att.net>]

Hello to everyone again.  I would like to thank everyone who replied to 
my first message about the check engine light on my Turbo 5000CS.  
Unfortunately, the problems have gotten worse.  A few days ago during 
the cold snap,  I started the engine to find that the boost gauge was 
registering 0.0 bar.  The engine seemed to run normally, but without the 
feeling of the turbocharger.  I drove the car for a few miles and 
suddenly, hitting a bump in the road, the turbo seemed to "click in".  
With a vengeance, as I briefly saw 1.6 bar on the boost gauge and the 
car felt like it had doubled its power.  

The next time I started the car, however, the boost gauge again 
registered 0.0 bar, where it stands now.  Also, the check engine light 
continues to come on whenever the engine surpasses 3,000 rpm; it 
switches off when the rpm's drop.

A local mechanic suggested that the turbocharger might be stuck, 
refusing to turn except when "broken loose" by a bump.  How can I 
determine if the turbocharger is spinning?  If it is truly stuck, 
wouldn't this affect the smooth operation of the engine (the car is 
perfectly drivable now, just not as powerful)?  If it is spinning, why 
would the boost gauge register 0?  Finally, if the turbo is shot, can I 
purchase a rebuilt one or have mine rebuilt and what is the approximate 
cost of this?

I know this is a lot of questions but I would really like to pin down 
the source of this trouble as the rest of the car runs and looks 
terrific.  Thanks in advance once again for any suggestions or comments.

David Kowalski