Date:         Tue, 21 Aug 2007 19:18:14 -0700
Reply-To:     Evan Mac Donald <macdonald1987@SBCGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Evan Mac Donald <macdonald1987@SBCGLOBAL.NET>
Subject:      Re: Rough running till warmed up
In-Reply-To:  <20070821222839.BD3171165C3@hamburg.alientech.net>
Content-Type: text/plain; charset=iso-8859-1

Yes, you are correct in a sense. I should have said that this is an unmeasured and unregistered by-pass, that is variable by its own schedule only, and cannot be taken out by any normal adjustment.

  And remember the airflow sensor is NOT used at idle. That is what the idle compensator computer and cut-off switch are for. So, it does count as a leak. It is not venting the plenum directly to atmosphere, like a "normal" vaccuum leak, true, but it is not being metered at the adjustment screw, just merrily flowing past, unregulated.

  The airflow regulator can be disconnected, and even removed, and the engine will still idle. The airflow volume is too low at normal engine idle speeds to accurately measure using this method, so they don't try. That's why there is a separate idle control circuit and computer.

  Mike S <mikes@FLATSURFACE.COM> wrote:
  At 06:02 PM 8/21/2007, Evan Mac Donald wrote...
>The butterfly plate in the throttle could be worn, and the shaft and
>plate do not settle into place properly. This will have two major
>effects. One, the throttle plate will not seal off the throat of the
>throttle body properly, so you in effect have a HUGE vaccuum leak.

Just a clarification. That would not be considered a vacuum leak,
because anything leaking past the throttle plate is still measured by
the air sensor, so the mixture remains correct. A true vacuum leak
results in a lean mixture, because it's not being measured.

It would result in a varying and difficult to set idle, though.