200T problems, new turbo needed?

[Heikki Pikkujamsa <100655.2526@CompuServe.COM>]

I bought a '89 200T about two months ago, got it cheap because it nedeed a new
pwr steering pump and a brake booster. Fixed those and learned to live with 3
pwr windows and "floating" speedometer needle, when it happened. I was making a
pass in a freeway when suddenly, instead of that comfortable power, the engine
generated a lot of black smoke which could be seen from the rear view mirror. 

After that incident the car hasn't been the same allthough I haven't seen the
black smoke anymore.  It stalls if I have to stop in red lights engine hot, and
does not start until after 10 minutes or so. Another alternative is to open the
air filter box and pump the air flow meter flap to get some gas to the
injectors, and then just drive away. Also, the car generates speed very slowly
now and the tachometer hardly goes over 5000rpm even if I floor the pedal (max
boost is now 0.9bar, before it was 1.3 bar). Another sign of problem is that the
vacuum assisted idle stabilizer system does not work.

I would preciate if someone could give me advice on what might be broken. I
think that the turbo gave up and it is actually rescricting the airflow thus
minimizing the flow meter flap movement. On the other hand could faulty ox
sensor cause something like this? I haven't found any leaks or cracks on the
turbo/cooler piping. 

If the turbo has to be replaced I would not mind to upgrade it to a bigger one
or use some KKK hybrid similar to Garret TO3/04 combo's which are very popular.
Anyone tried this? Also, does anybody know how much airflow (hp) is the stock
KKK capable to produce and where lies the limit for the stock CIS? As I
understand that the actual boost in stock rim is only 0.3 bars, I believe that
this little powerplant has a lots more potential than 170hp.

Any suggestions regarding the problem are more than welcome.

Heikki