Date: Sat, 27 Jan 2001 22:23:41 EST
Reply-To: CMathis227@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Chuck Mathis <CMathis227@AOL.COM>
Subject: Re: '85 1.9L Stumbles Off Idle When Warm
Content-Type: text/plain; charset="US-ASCII"
In a message dated 1/27/01 7:23:57 PM, gstearns@OPTONLINE.NET writes:
<< A suggestion with no guarantee of success: connect a digital voltmeter to
the output of the O2 sensor. The output should fluctuate which is normal,
but if it's going much below .45 to .50 volts, she's running too lean. Our
'88 had a massive idle stumble for several years (sounded like a race engine
with a wild cam that would barely run below 3,000 RPM) before I figured this
out. Tried everything that you have and more with no success 'til I found a
solution. Funny thing is it passed emission inspections well below standards
even while stumbling away. If you find that the voltmeter says she's
running lean, maybe time to change the settings in the AFM. The AFM wiper
can have it's static setting changed or it's spring tension changed. Sounds
like you will know where to look for these adjustments. My suggestion is
to move the static setting slightly richer. After using this, you may find
that you want to make the spring tension slighty tighter to keep it from
running too rich at greater throttle openings. We eventually ran our engine
"open loop" with the O2 sensor connected to a voltmeter on the dash, but not
to the ecu. Doing this taught me alot about digifant characteristics and
their effect on engine performance... **without having the O2 sensor trying
to undo what I was doing**. Our manual trans Vanagon can now almost have
the clutch sidestepped from a stop without a stumble. I don't know if what
I have done is an actual correction of the basic problem, or a band-aid that
helps the symptoms, but it has worked.
Gary >>
Gary,
The Digitool shows the O2 sensor at .41v at start up. As the engine warms up
it rises to .45v before it starts to fluctuate between .45v and .75v. Though
I know it's not a guarantee it is new so I don't think the O2 sensor is the
problem unless the very existance of O2 sensors is my problem. Cold idle is
pretty smooth but does pick up some rump-rump as the temp rises before it smo
oths out again.
Since I spent most of today doing my first coolant change -- what a special
task that is! I'll pull my plugs tomorrow. With all the exhaust leaks
causing it to run very rich before I changed the system they may be fouled --
I forgot to check the obvious first. I'm going to check the tolerance on the
throttle position switch as well -- seems it might cause problems if it was
staying open too long. I have tweaked the AFM spring some -- tightened it
nine notches three at a time over the past three or four weeks. Maybe more?
Chuck
