Need help with '88 300E peculiar idling problems?

[Steve190E 2.3]

I am going crazy here with my 88 300e(w124). My idle is too low at initial start up. Once warm it has a mind of its own. Sometimes it will idle high (only in park or neutral) and sometimes normal. I tryed adjusting the air/fuel mixture but at pin 3 on diagnostic connector I am getting almost 12v even with O2 unplugged. The idle switch is working fine. The car has been boosted a couple of times. Does this sound like classic overvoltage protection relay? Any help or ideas where else to look would be greatly appreciated. I don't want to go through the car and spend a pile of money to find the problem. I appreciate all the help I have had on this forum and think that this makes a benz more affordable.