'83 Spider (Bosch EFI) questions, yet again

[Bill Bain <BBain@IMNET.com>]

Well I'm still struggling with getting my '83 to run right.  This
weekend, before the Sunday storms and rains (Bill Harkell, are you all
right?), I checked as many of the sensor values as I could:  O2 sensor,
coolant temp, AFM, etc. All values observed but one were right where
they were supposed to be. The only one that appears out of whack was the
O2 sensor, which is newly installed two weeks ago.  It fluctuated
between 0.697 and 0.737 volts on the DVM (and a o'scope) at idle (800
rpm)  (back probled into the connector, exhaust manifold as ground --
there don't seem to be many good grounding points on that side of the
engine bay).  Connecting and disconnecting the O2 sensor produced
noticeable fluctuations in RPM, with RPM going up when the sensor was
connected.  Observed mileage with the sensor connected:  14 mpg, 21 mpg
disconnected (mixed driving).  Misses above idle with the sensor
connected, does not miss above idle (at least so I can notice) with the
O2 sensor disconnected.  Questions:

If I understand what the O2 sensor is telling me, it seems that the car
is simply set up too rich, since if the value changes, but is
consistently above 0.45v, that's an indication of an excessively rich
mixture.  This would be consistent with the fact that if there's no O2
sensor voltage connected, the EFI reverts to assuming a 0.5v signal,
which would be a "leaner" signal than what the sensor is actually
putting out.  What am I missing, and how does one adjust the mixture on
a Bosch EFI system?  One can adjust the air bypass on the AFM for idle,
but how 'bout above idle?

I confess to being a bit baffled at this point, and if I can't figure
this out pretty quickly, I'm going to revert to "checkbook mechanic" and
take it Hans and let him figure it out.  Any help would be greatly
appreciated!

Bill Bain
Atlanta GA
'83 Spider (hiding in the garage from the bad weather!)