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Help! No stable idling on 1981 4000

  Happy New Year to all!
I'm new on this list, but hopefully somebody will know the answer to my
problem.  I have an old Audi 4000, 1981, 4cyl, MPI, manual transm.
This car cannot idle at a stable speed until the engine warms up (about
2/3 of the thermometer scale).  Until then I have to keep accelerator
depressed to keep it from stalling.  The other solution is to increase
the idle speed by turning the idle speed screw on the throttle assembly,
but then, of course, when it warms up it stabilizes around 1100-1300 rpm,
which is terrible - the engine runs hot, waste of fuel, etc.  
I've tried many things: checked thermoswitch, checked and tried replacing
the fuel pressure regulator, checked cold start valve - all of those
things were functioning.  I talked to several people, opinions vary.
Some say that the electronic control unit for oxygen sensor needs to be
changed, others suggest, that it is a faulty fuel distributor or frequency
  The problem is only with idling.  When accelerator is depressed and 
engine is loaded everything works fine.
  I would appreciate any advise, even though I realize, that cars discussed
on this list are mostly new models.

Best wishes to all Audio enthusiasts in 1996!

Filipp E. Kistenev