james-your posts imply that you know this, so don't think I'm discounting you.
20 mA is the lean running enrichment limit for CIS-E. Either the fuel distributor needs a big adjustment in the rich direction until this comes down into the 10mA region and starts ranging or there is a problem. If you unplug the sensor, the current should default to 10mA. If it does, try adjusting CO w/it connected-see if you can get it into spec. If it doesn't, measure the reference voltage of the oxygen sensor circuit into the ECU-disconnect the sensor from the large male connector, and check the voltage of that male connector and a good ground connection on the engine (valvecover stud). You should see less than .6V; anything more than that is a problem and probably caused by a resistive or absent ground circuit between the ECU and the engine, which will cause the ECU to track to it's full (20mA) stop. If the reference voltage is OK, you can confirm that the ECU responds to a signal by grounding that connector (the ECU will see a lean signal and increase the current to counter it, adding fuel) or, holding the connector in one hand, grab the positive terminal of the battery, driving the current the other way to zero. If the reference voltage is too high, it will still respond the same way to this test, but still won't work properly with the sensor connected, you'll need to find the grounding problem and fix it before proceding. (try watching the reference voltage while disturbing the wiring-when you improve a ground fault, you'll see the reference voltage drop to .5v or so). if the reference voltage is OK, the system goes to 10mA w/o oxygen sensor connected, and richening the airflow meter (turn clockwise) doesn't bring the current down, you need a new sensor.
ps: the only reason I'd want to have my sensor working would be so I could have a starting point for tuning. You must also be sure that the full throttle switch is working-that w/oxs disconnected, engine warm, DPR @10mA, that when you close the full throttle switch, the current jumps up (between 2 and 5 mA as I recall-depends on which ECU you have-1.8 16V preferred) You'll certainly need to adjust the thing quite rich without any (illegal?) fuel enrichment device. Having a functional oxygen sensor will also be helpful to compensate for that richness when you're off full throttle or idling. Hope this helps. regarding timing-12* is a little overadvanced if stock advance is working, and 18* too little if you are checking at full advance.
