how would I know what is normal voltage or desired voltage?

0.45 volts (450 millivolts) is suppose to be the ideal (air:fuel of 14.7:1). Lower voltage is lean, Higher voltage is rich. ALL O2 sensors work the same, it's just the vehicle application that's different. That means it'll cost you less for the same sensor in a mustang than in a MBZ because the quick disconnect plug is different and maybe the size of the hole it's threaded into.

BTW the Fuel:Air adjustment screw is VERY sensitive. Work in fractions of turns of the adjustment tool.

Intruder

Deeph8 in your post you said you tried my way, but you used pin2 of the diognostic sockett, it has to be pin 3 and also the car must be at normal opertaing temp with all accessoies switched off, this way is the simplest way of adjusting the mixture and has given me excelent results, if you cannont obtain the voltage reading between 6.8 and 7.2 volts dc the fault may be the coolant temp sensor located at the rear of the head that has 2 round conectors pluged into it, i`ve been told that this can cause the reading not to be obtained this infomation was given to me by Australia`s most highly regarded Merc guru. I bow to his wisdom every night before i go to bed!

Pin 3 on the diagnostic connector on my 280e is a null. It doesn't seem to be connected to anything. Is your diagnostic connector round and on the left side of the engine compartment?

Yes it`s on the left side, it has a screw off plastic black cap and has 8 or so holes numbered 1-8. The other side of the d.c. volt meter must go to battery minus.

Just use a vacuum gage. Connect to manifold vacuum and adjust till maximum vaccum is attained. That will be the idle that you want.