Your readings are more than confusing.

One milliamp equals 0.001A. So, 0.25ma = 0.00025A. Are you sure about the decimal point?

To calibrate you test technique, one must go for one of the fixed readings. Key on, engine off, is usually 20ma (it can be 10 ma or one other value... it is not optional but they did it differently on different models; most are 20ma). The O2 sensor disconnected while running should produce 0.0ma.

Probably the most informative view of whats at stake is the lambda range test. To do the test get the motor idling as best one can with mechanical adjustment with the O2 sensor disconnected. Then take the O2 sensor output lead (the one you disconnected from the sensor - it goes to the controller) and jump it to ground. The controller sees 0.0v O2 output and slowly moves the EHA current to correct. This signal, 0.0v O2 sensor, is interpreted as a lean mixture and after all the capability to correct is finished you should see around 12ma EHA current (plus current gives enrichment).

Now go for the other way. A "D" cell battery would do the trick but it is even easier. Take one hand and contact the O2 sensor output lead we have been working with and place ones other hand on battery voltage (DO NOT hook the sensor lead straight to the battery... go through your body). The small potential making it through your body will fool the controller into thinking it is seeing hi O2 sensor output voltage and it will lean out the mixture by going negative 12ma EHA current.

From these basics you may see my problem with your figures. First .25ma is inconsequential. The 0.0ma I give for the open loop (disconnected O2 sensor) is likely to be more than .25ma off of zero just due to meter calibration or even controller variables. It never controls at that level. This could mean you are really reading 0.0ma all along. The difference between +0.25ma and -0.25ma is inconsequential. The controller would see it as zero.

If you are off one decimal point you are twice the values I give for max readings in either direction. A very likely senario could have 12ma at idle and -12ma at both other rpm ranges. Such a group of readings would be characteristic of a vacuum leak. It would take full mixture correction at idle but that correction would leave it too rich at the higher rpm where the leak is small in proportion, thus the minus readings off idle.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician