Failed Emissions Test

["eroe@domain.elided" <eroe@domain.elided>]

I recently went through a similar problem with my '87 Milano (110k miles). 
Here in Oregon, the test is free if you fail and there are no "gross
polluter" laws.  So, I fixed the car myself with no fear of long term
consequences.  My car failed idle but passed the high speed portion of the
test (the car is run on a chassis dyno during the test).

I found some interesting things.  Primarily I found that the CO adjustment
of the air meter did have to be dialed in.  Before I worked on the fuel
system I went through the ignition.  Please do the same!  Anyway, the plugs
had 24k miles on them (Lodge) so I put new ones in.  I checked the plug
wires for continuity and all were fine.  Finally I set the timing up to
factory specs (F mark on the pulley at idle).

After I finished that work, I started on the fuel system.  I put a DVM
(digital volt meter) on the output from the O2 sensor.  With the sensor
hooked to the FI ECU, the car hot (fan had cycled several times) the reading
was almost zero!  The O2 sensor measures the amount of oxygen in the exhaust
as compared to the atmosphere.  A reading of zero indicates a very lean
mixture.  I sprayed a little WD-40 looking for vacuum leaks and found none,
so I decided to adjust the CO bypass.   

I disconnected the sensor from the FI ECU and watched the output on the DVM
as I turned the bypass.  Since my initial reading was very low, I turned the
bypass CW to reduce the idle air flow and enrich the mixture.  You must keep
the sensor hot during this procedure, so every 15 seconds, run the engine at
about 3,000 rpm for 5 seconds.  The sweet spot is small, so be patient as
you adjust.  Keep at it until you get a reading of about 0.5 volts
(remember, the FI ECU is NOT connected to the sensor).  Rev the engine up a
again and recheck the output.

Upon a steady at 0.5 volts at idle, hook the sensor back up to the FI ECU,
but keep the DVM hooked up.  Now the value will swing from about 0.25 to
about 0.7 volts as the ECU controls the mixture.  Before the adjustment, the
air flow was to far out for the ECU to compensate.  However, at higher
speed, the ECU deals with much more air and has an easier time of keeping
the mixture on track.

After this quick tune up the car easily passed the test.  It idles much
smoother now as well.  As noted, it is very important to have the car HOT
before the test.  Run it on the freeway in 3rd for a while to ensure
everything is hot.

Please visit our web page for more details:
http://www.alfaclub.org/techstff/oxymoron.htm

Erik Roe
AROO newsletter slave (editor)
'87 Milano, some old spiders & a '82 VW Westie with a '94 Jetta 2.0l engine

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