[alfa] Re: Fast Idle

[Michael Tiefenback <tiefenback@xxxxxxxxxxx>]

Chris Sasso wrote:


     Date: Sun, 01 Aug 2004 17:27:06 -0400
     From: "Chris Sasso" <Chris.Sasso@domain.elided>
     Subject: [alfa] fast idle

     Hi All,

     My '87 Spider would not start so I went through the protocol
     to test
     the various Bosch FI components.  I ended up finding the
     Auxilliary Air
     Valve closed when cold, so I loosened the nut forced it open
     (per
     www.oldebottles.com)and tightened the nut. My Spider started
     instantly
     on the first crank but now has a fast idle.  Is the Aux Air
     Valve
     possibly causing this fast idle?  I'd rather not by a new one
     for $250
     if I do not need one.  It did not idle fast before the fix
     although it
     was very difficult to start.

     Also, when cornering I get a hesitation as I accelerate out of
     the
     corner.  Any thought on the cause?

I went through all of this logic recently, so I'll give you the (however
dubious) benefit of my present understanding.  The AuxAirDevice (AAD) is
a bypass around the throttle for metered air.  The throttle should be
_closed_ when it is supposed to be closed.  You might want to start
there, and with the throttle sensor switch.  The AFM should accomodate
all of this air flow with appropriate fuel.  The idle throttle
adjustment (which check) is another bypass for metered air.  The idle CO
is a bypass for _unmetered_ air to help correct any deficiencies in the
AFM and O2 sensor functions at idle (low flow).  The AAD is set to
satisfy the need of the engine for more air when it is cold.  The ECU
supplies proportionally more fuel.  It must be temp dependent, or proper
cold idle settings will give too high a warm idle.  The oldebottles page
suggests cleaning out the AAD periodically with solvent.  Try setting
the warm idle with the idle adjustment, and get a grommet for the
insides if you don't have one.  I didn't.  The interplay between the
fixed idle air bypass and temp-dependent AAD is probably not set right
for your car.  And you might need to muck with the idle CO, too.

Test the AuxAirDevice per the directions.  Replace the tube if it's too
stiff to survive being pinched.  Check your O2 sensor reading.  The only
real reason for stumbling on acceleration would be a lean mixture, if I
recall correctly.  Your AFM might be a bit off.  The one in my '86 had
seemingly been the benificiary of attention from the P.O.  I had to
apply some corrective attention.

If the AAD doesn't work properly, they can be had on ebay occasionally
for some tens of US$.  Greg Gordon (oldebottles.com) sells a manual
valve to replace the electrically actuated AAD, if that's not too far a
step backward for you, a la manual chokes. for a similar price.

Michael
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