200 10V stumbles, poor mileage

[Konstantine Bogach]

Hi all,

my 200 MC2 stumbles at idle or when I increase RPM, until I am at 3000 
rpm.  Above 3K I don't feel stumbling.  All plugs are same wet and 
black. Coil resistance,  CIS system and control pressure are within the 
spec.  Can not see a vacuum leak anywhere (also did carb cleaner spray 
test).  But I don't think it is a leak b/c at higher boost it runs 
better rather than worse.  Inspection of ignition distributor cap did 
not reveal a clue (I tried the spare one too.)
  Almost not working in cars last 2 years I forgot what I had learnt 
before (mostly from this list).  What I should be looking next?  Can 
broken soldering in the throttle switch cause such symptoms ?  Hall 
sensor?  RPM or crank position sensor?  There is no codes stored.

All ideas will be appreciated.
Thank you.
Konstantine
200 '91 & UrS4 '93.