I'm going to beat you guys till you understand this.
If you start at zero or wind up at zero with the early 190 system then the system is pegged. For the only positive current systems the nominal adjustment would have you at 8ma. Again pull the O2 sensor and you will see the middle of the road position for either system. The 190 will go to 8ma and if you ground the sensor input to the controller the system will correct to its capability 16ma. if you do the voltage through the body bit you will have it removing enrichment and it will bottom at zero ma.
What you have to remember is that in a perfect system the needed correction at idle would be the same as at 2000 and at 4000 rpm. The correction due to feedback (O2 sensor is in the exhaust and its is after the fact  feedback) should only affect discrepancies to ideal. Other aspects of the system will change mixture. When you step on the gas, instantly the airflap drops. The speed and ammount is proportional to how fast and how much gas one gave it. The airflow potentiometer gives this reading to the controller and increases the momentary mixture correction (adds fuel correction) by adding ma. Sooo... at any point if you stomp the gas there will be an increase in current, once the moment is over the correction will go back to steady state correction which is buried in lean correction if at zero ma on a positive current only 190 system. I think this 190 system stopped in 1986, so don't the rest of you get confused. They quickly decided that better control and a much superior limp home was achieved by having plus/minus current correction.
The plus/minus correction allows zero ma to be the center and a well adjusted car that looses electronic control does great in limp home since all steady state mixture would be at exactly where it was supposed to be anyway  zero. The pos only systems are in the middle at 8ma, when electronic control leaves it goes to zero current and this is the maximum lean correction which doesn't make a good limp home condition.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
