1987 260E

2 problems

1 I'm having trouble getting a reading from my 02 sensor. The old sensor did not respond like I'm used to seeing, engine warmed up and a fluctuating reading between .02 - .09 volts. I bought a new Bosch sensor and still get a constant reading of about .92 volts. The heater circuit is fine. ?????

2 This is a contiuation of the 02 situation in that I cannot get a duty cycle reading as the vehicle is not going into closed loop.
If I disconnect the eha and the idle control then adjust the fuel with the 3mm allen wrench to the highest idle and vacuum reading (1400rpm & 16") then reconnect both the eha and idle, why does the engine run slower and rougher, if the mixture was close to correct with these items out of the loop why does it need to change anything especially as the 02 sensor appears to be non functional.
Long post I'm sorry. I've spent hours going over previous posts, measured every component, but I've obviously missed something.
Gentlemen, I need your help.
Michael

An O2 sensor that reads .9V means the mixture is too rich. Try leaning out the mixture.

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Thank you for replying,
the second part of the post explained that I leaned the mixture out with eha and icv disconnected to the point where if I turned the 3mm allen wrench anti clockwise any more the engine started to lose rpm's and try to stall, too lean?. Is it possible the mixture screw can be a whole turn too rich. Is there a starting point, similar to carbs. (where you screw the mixture screw all the way in then back it out2 turns) Is there a stop point on the 3mm screw?
I don't know if the previous owner turned the screw all the way in or what.

Thank you,
Michael