91 100 Rough idle and no throttle response after warmup - Solved!

[SJ]

Huw wins the fair maiden for his correct diagnosis - -> defective Oxygen
sensor.

The problem was the oxygen sensor. I had to drop the catalytic converter to
get at the oxygen sensor. Of course, the cat hardware was replaced with
Stainless Steel, ala Huw.

There was a dramatic difference in performance after installing the new
oxygen sensor. Car had lots more Ooooomph! The old sensor looked pretty
ratty. I think it was the original sensor(100K plus miles).

With the new oxygen sensor , the sensor voltages and fuel regulator current
readings are:

Ignition on    -  reg current at 100ma, O2 voltage at .5v (This voltage is
provided by the ECU)
Start            -   reg current at 70ma, O2 at .6v
Warmup       -  reg current steadily drops to 3ma , O2 voltage stays steady
at about .7v - then starts swinging between .2v and .9v as system goes into
closed loop mode. Time to closed loop was about 3 minutes.

I found an article at       http://www.mr2.com/TEXT/O2_Sensor.html     which
explains how to test the sensor on the bench. I tried the technique and it
worked. I tested the new sensor before installing it.

I paraphrase the article below:

1. Clamp O2 sensor in vice, attach digital DC voltmeter to sensor. Gnd to
sensor body, Pos to black sensor lead.
2. Propane torch set to high, heat perforated sensor tip - - should see at
least .6V within 20 seconds.
3. Remove heat - - voltage should drop to under .1V within 4 seconds.
4. Heat for 2 minutes and watch for drops in voltage.
5. Move the flame back and forth over the sensor - voltage will quickly
change from high to low.

Test Summary: Any sensor that generates 0.9 V or more when heated, show 0.1V
or less within one second of flame removal, and pass the 2 minute heat test
is good regardless of age.

Now I need to figure out how to reset the radio code . . .its on "SAFE".
Fix one thing and find two more things to fix. I doubt the car owner has the
code for it. Looks like a trip to the dealer so that they can pull the radio
and look up the radio serial number on the computer to get the code. How
much do they charge for that?

SJ
88 5kq
90 100q

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
.
> I hooked up an ammeter to measure Differential Pressure Regulator Current.
> And I hooked up a digital voltmeter to the oxygen sensor lead, oxy sensor
> connected to harness connector.

> 5min 30 sec - reg current at 15ma, ox sens at -.5v
> 6min 30sec - reg current at 20ma,ox sens at -.5v
> 7min 00sec - reg current at 18ma,ox sens at -.5v
> 7min 30sec - reg current at 3ma,ox sens at -.5v

> Now I have to figure out what all this means. I think the oxygen sensor is
> bad.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - -

Me too.  The OXS voltage is supposed to fluctuate steadily over a few
second cycle, up and down around .5 volts.  Yours appears to be locked
into .5 v, which is probably due to the presence in the ECU of a "ghost"
voltage produced by the circuitry therein (you should be able to measure
this .5 v at the OXS harness, ECU side, with the OXS unplugged).

with it unplugged you should run ok, in the fairly decent limp home mode
of CISE3 (defaults to 0 mA).

with it working, the DPR current should flustuate as the OXS voltage
does, above and below 0 mA, btw.

--
Huw Powell

http://www.humanspeakers.com/