Mike,

You have three adjustments to the Fuel Injection sytems, and Four other
inputs that affect mixture.  And as pointed out  by others the
compression, vaccum and other engine conditions can affect unburnt HC.
Since the O2 sensor "controls mixture" it can cover a range of off spec
conditions.  In order to adjust the system it must be taken out of the
loop until the values are adjusted.  and I don't thnk the O2 is really
cabable of control mixture that well at idle, hence the AFM Mixture
adjustment. Proably not enough gas flow per unit.

I have written procedures in the archives to tune the Digifant fuel
injection, just search kelphoto, I've used that since I joined the list
in 1997,

The adjustments are, spring tension- affects overall mixture at every
rpm, so it should be set first and under load, see below.
The Idle Air Screw on the throttle body, adjust idle speed only with NO
Mixture effect
The CO mix adjustment on the AFM, which affects mixture at idle only.

 The complete instruction in the archive should be followed but short
overview is: is set the spring tension at road speed, warm engine, NO
O2, aim for .5 volts at or above 3000 RPM,

Then at idle with no O2 and No idle control warm engine, set the idle
speed,  then set the CO mixture to read .5 volts on the O2.  This works
according to Probst on Bosch Fuel Injection, because happily enough 5%
CO and .5 volts O2 are near each other in their respective scales.

The fixed inputs I mentioned:
TEmP II, coolant sensor, I prefer the OEM one
The Fuel Pressure Regulator, 29 psi at idle vaccum and 36 psi at no
vaccum, are the guideline values, give or take a couple of pst.
The Temp I sensor, ( but only on cold Days).
The O2 Sensor, I prefer NTK brand

I hope this clears up some of the sequence of what to do, which screw
does what.

Mark Keller
91 Carat