RE: daily update

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> > also, noticed a new unusual behavior.  the car
> > seems to not want to let go of the idle speed
> > when i clutch in - between gears or coming to
> > a stop.  it takes several seconds for the revs
> > to drop down to idle speed once i stop.  the drop
> > is a slow, smooth decline.  i am going to check
> > the throttle linkage stuff, but i thought there
> > might be a good btdt from y'all.
> 
> You fixed something.  This is what it's supposed to do - or at least,
> it's what the ur-quattro ISV controller is supposed to do, and I think
> it's the same part.
> 
> Idle is 800 rpm at rest - optimised for low vibration.  It's raised if
> the battery voltage is low or the a/c is on.  The ISV will _not_ allow
> idle to drop below 2000 rpm if the vehicle is moving - it assumes you
> might need the power steering or the brake accumulator refreshing.
> 
> If you knock an ur-quattro MB (equivalent to the MC engine) out of gear
> and coast gently to a stop, the idle drops in specific stages and
> finally drops to 800 rpm some seconds after the car comes to a halt.
> 
... for better or worse, Rocky lives here in the good ol' USofA ... which
means that unless his car was modified by a P.O. it is equipped with the WX
motor ... which might map somewhat to the WR with which you may be familiar
... the only sort of idle speed control that the WX motor has is a timing
advance that the ECU kicks in if the idle speed drops too low.  Cold engine
throttle plate bypass is controlled by an Auxiliary Air Regulator (AAR)
valve ... it has no ISV.  

I think that Rocky has pretty much nailed the possibilities ... something
may be sticking in the throttle linkage (don't discount the cruise control
actuator).  Newer turbos such as the later MC engines had a dashpot on the
throttle body which prevents the throttle plate from closing abruptly, but
the WX doesn't have this mechanism either.  In trying to think about other
oddball faults that might cause the idle to drop slowly ... perhaps the high
vacuum condition in the intake manifold is causing one of the throttle valve
bypass valves (AAR, valve that provides bypass when the A/C is on, etc) to
be drawn open and bypassing the throttle body ...

HTH!
Steve Buchholz
San Jose, CA (USA)