CIS problems. High CO on emission test.

[Konstantine Bogach]

Hi.
My time came to pay dues to CIS gremlins.    It started when I did not
pass emission test - CO is 0.7 (whatever units they use) while limit is
0.5.
I did not think much - changed wires and spark plugs - anywhay they were
due to and I found that one wire was broken.   It did not pass test
again.  The patient is 200tqa '89.
Driving with duty cycle meter hooked up to CIS test connector I found
that I can not fix the duty cycle.  At first look it turned out  to be
70% at idle,   I adjusted the screw to ~50% (engine is warm,  numbers
are average values ).  Raise rpm several times,  checked - 50% at
idle.   After driving several minutes  I noticed that idle duty cycle
fell to ~30% at idle.   Adjusted again to 50%, drove several minutes -
70% at idle.  Again: it is all on warm engine.   I tested TPS - good,
its wiring is good,  wiggling wires at connector did not changed .2 Ohm
between TPS connector and ECU connector.  Checked air temp sensor - good
(resistance ~500Ohm,  no broken wires observed,  wiggling test was
passed).   No vacuum leaks.  By the way,  rubber cap from plumbing in
Home Depot is like made for intake pipe.  Plug intake side and you can
pressurize whole system except intake rubber boot over air flow
meter.    So, I checked vacuum leaks - no leaks.
Checked fuel system pressures - in spec.  Residual pressure holds very
well which means injectors do not leak, right?   It also means that fuel
pressure regulator do not leak as well, right?  So, I need to find
another explanation for longer cranking if the engine is shut off for
more than 30 min.
This "binary" state when duty cycle rocks between ~30% and ~70% makes me
think that ECU is faulty.   OXS is relativly new - 15-20 Kmi.  I looked
at OXS signal on oscilloscope and it looked fine.

My second 200tq '89 did not pass emission test with same results  -
CO 0.7  but in this case duty cycle is stable on ~50%.   I did not look
at this one yet.   It is just to add to drama :)

I wonder what content of CO in the tail pipe other people have?
Does anybody in central NJ of Phili area have gas analyser or can
recommend a mechanic who knows CIS well and, preferably, will let me in
the shop?

I will appreciate your comments and advices.
Thank you.

Konstantin.
Hightstown,  NJ.