The setting of the idle mixture adjustment screw and even the operation of
the air flow meter can be somewhat tested using the O2 sensor. The screw
should have almost no effect at any speed above say 1200 to 1500 rpm. The
throttle switch should be closed when the throttle is closed or at full
throttle, not in between.

With the O2 sensor disconnected from the ECU, the ECU will use RPM and the
AFM to set fuel mixture. Measuring the voltage from the sensor to ground
will give a reading. You may have to drive a bit to get the sensor warm
enough to work. Ideally you should see ~.5 volts. If you rev the engine and
then close the throttle to activate the switch you will see the sensor go to
0 during fuel cut off. In normal operation the sensor is ignored for a short
period after fuel cut off. This is why that idle surge occurs if all the
basic settings are not correct.

Surging during closed throttle indicates that some combination of air and
fuel is getting into the engine when it shouldn't. Vacuum leaks after the
throttle or AFM can account for the air. Fuel can be leaky injectors or even
oil getting sucked past the rings or intake valve guides. Those white
crystals on the spark plugs could be oil or antifreeze. I suggest oil
analysis just to be sure it is not antifreeze.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
neil n
Sent: Thursday, June 21, 2012 2:36 PM
To: vanagon@GERRY.VANAGON.COM
Subject: CO Adjusting Screw. PO Set it All The Way In? Base Setting?

Hi all.

The protective cap on the CO screw was drilled and tapped. Checked CO screw
setting. It's all the way in.

Emissions test results seemed quite low (HO, CO, NOx), plug colour was grey.
Image:

https://lh3.googleusercontent.com/-HsjvHzL5ew0/T6iOlOpuTII/AAAAAAAAFvI/Gox0n
zYwBXg/s640/1988%2520Westy%2520Spark%2520Plugs%2520.jpg

Engine has a pretty consistent surge coasting in 2nd or 3rd gear @ ~ 2500
RPM down, and a mysterious stall, engine cold. Stall happens once. When
engine temp higher, engine runs "ok".

Reading this post from Dennis:
http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind0201A&L=vanagon&P=R7346&m=1551
77
I have to wonder if the CO adjustment is currently affecting the fuel shut
off process thus causing surging. A fuel cut off issue was one of my
original thought towards the surging issue.

I've done a full tune up, new O2 sensor & cat, cleaned grounds, repositioned
AFM wiper, adjusted throttle valve switch. (it consistently closes just off
idle), swapped idle stabilization module (old one causes idle issues when
swapped back in).

I don't have a sniffer, CO port is badly corroded.

I've seen posts in archives suggesting a base setting for CO adjust screw is
anywhere from 1.5 to 3.5 turns from seated in.

Can anyone confirm or suggest a base setting?

Hopefully a sniffer inserted in the tailpipe will suffice to check my work.

Thanks,

Neil.

--
Neil n

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