Date:         Mon, 6 Oct 2003 12:14:30 -0700
Reply-To:     Doktor Tim <doktortim@ROCKISLAND.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Doktor Tim <doktortim@ROCKISLAND.COM>
Subject:      Re: Idle/mixture Screw
In-Reply-To:  <20031006171143.95919.qmail@web14311.mail.yahoo.com>
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At 10:11 AM 10/06/2003, you wrote:

>That is the co screw, and it must be set with a
>exhaust gas analyzer, I've got mine messed up the same
>way, when I get it fixed I'm going to plug the hole,
>no more playing with it, I can't find anybody with a
>analyzer right now to adjust mine, good luck with
>yours. Phil

Let us assume that when the adjustment screw was last set, it was after
eliminating all weaknesses in the FI system and properly adjusted to spec
with an exhaust gas analyzer. If you are going to play with that screw
despite my advise not to, do this first. Carefully count and record the no.
of turns to turn it to it's seat. That way, you can always turn it to the
seat, then back out the proper no. of turns to reset it where it was to
begin with.

If the current setting was correctly done initially and you begin to have
running issues, turning the adjustment screw at best will just compensate
for the weakness/es developing elsewhere that are causing the change. Poor
response to adjustment if proof of faults elsewhere, and can only be noted
with an exhaust gas analyzer when these weaknesses are first developing.
You just cannot tune them by ear as is correct with carb adjustments.

I think it would be very difficult to find any reputable repair shop that
didn't have an exhaust gas analyzer. It is an essential tool without which
you will never get a rep for precise tuning always. Competence cannot be
had without it.

Moreover, turning the mixture adjustment screw will not resolve anything to
do with:

Cylinder compression balance out of spec.
Fuel pressure out of spec.
Temp sensor out of spec.
Pressure regulator out of spec.
AFM out of spec.
Poor grounding of any of several items.
Vacuum leaks
Heavy deposits on valves or throttle body
Poor throttle switch
Sticky bypass valve
Plugged breather
Dirty air filter
Dirty fuel filter
Fouled or worn plugs
Weak spark for any of several reasons

That's just off the top of my head. Bottom line, all else must be verified
in spec prior to the final adjustment WITH an exhaust gas analyzer. Always,
verify complete maintenance is up to date. If that doesn't resolve your
issues, only then proceed with further diagnostics. In many cases, further
diagnostics will be unnecessary. You will already know why you have poor
mixture response or you will make the final verification of good response
to precise adjustment with aid of the proper instrument to measure the
adjustment.