At 06:55 PM 6/26/2010 Saturday, A J wrote:
>I assume that since the wires are not connected to any sensor that the
>circuit is open and sending a fault reading to the ECU and the 1.9 is
>running in default mode. If I temporarily jumper the wire so it would
>seem connected to a sensor would the ECU the assume the o2 is
>functioning properly and resume its normal running mode.

Dear A J,

Bad assumption.  If you short the O2 sensor leads the ECU will drive
the mixture unbelievably rich.  When you're having a sensor problem,
or any time you have any problem at all and are trying to diagnose
it, simply unplug the sensor and leave it that way.  The ECU will as
you say interpret that as O2 sensor missing or not yet up to
temperature, and will run in open loop mode.  However this is not a
fault mode and with the sole exception of emissions the engine will
run entirely correctly if all its bits are correct.

Unlike newer ECUs this one has no "limp home" mode.  As I said,
open-loop is not a fault mode and in fact the European "Vanagons" had
no O2 sensor and needed none; and the ECU always ran open-loop.  The
sensor and closed-loop operation are entirely related to giving the
catalytic convertor the very closely controlled mixture it requires
to properly balance the three stages of conversion it performs so as
to give minimum HC, CO and NOx.

Yours,
David