[T3] Throttle Valve Switch and AAR, etc.

[Dave Hall]

2-  The idle adjust screw on the IAD simply allows a bit more or less bleed
air in to set the idle speed.  The more air bleed that gets in the higher
the idle speed (until it reaches the point when the injectors don't fire and
the revs fall back again).

The AAR does just the same, but self-adjusts as the engine temperature
changes (apart from some automatics that had an electrically-heated valve).

These systems work in parallel - too much air-bleed from the AAR when at
operating temp will need the idle-speed screw backed off.  That may mean the
AAR gives too much air at start-up.  

If the AAR doesn't seem to be working effectively, take it out and clean
dirt off the spring.  It can stop it operating correctly.  It shouldn't be
necessary to readjust it. 
The spring is bimetallic, and turns the shaft valve as (ISTR) its coils
tighten up when warmed, so dirt on the coils can stop it functioning
properly.  (awaits correction on rotation sense!).

Note, the two air-bleeds simply reduce the IAD vacuum level (i.e. bring the
manifold pressure back nearer atmospheric, equivalent to opening the
accelerator a bit), and the pressure sensor detects this, so the brain opens
the injectors a bit longer to give a bit more fuel to go with the extra air.



Dave
UK VW Type 3&4 Club
===================


-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of J. Jonik
Sent: 11 November 2012 19:31
To: type3-vwtype3.org at lists.vwtype3.org
Subject: [T3] Throttle Valve Switch and AAR, etc.

Questions:
 1-    Setting the Throttle Valve Switch.   If the engine's running, and you
moved the TVS setting (with lower screw kept temporarily loose), should you
notice any change in idling when it is in incorrect setting?    If there's
no change (as it is with mine), does that mean the TVS is shot?

2-   Setting the Alternate Air Regulator.... To get this straight...is it
that when it's cold you can blow through it freely, but when it's warmed up,
the spring closes the passage and you can't blow through it?
  So, if setting is wrong, and air continues to go through, will that cause
irregular idle, or just slightly speeded up idle?

3-  I want to test the ground wire on top center of the engine to make sure
it's not broken somewhere.   Can I use test light to touch to a hot wire and
to the un-plugged ground wire to see if it lights?    Or, will I fry
something?   (I'm not a whiz at electronics.)
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