Date:         Mon, 5 Aug 2013 14:45:50 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Idle Surge
Comments: To: Bryan Feddish <uprightbassghost@HOTMAIL.COM>
In-Reply-To:  <BLU162-DS21BEB2ED48E50968BEE14FCE5C0@phx.gbl>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 02:14 PM 8/5/2013, Bryan Feddish wrote:
>>>Tell us in detail about the symptoms? <<
>
>After the engine warms up the idle just goes up and down about every second.
>If I'm missing some helpful details let me know.

If it's just a slight alteration in exhaust note, that's normal
behavior from the oxygen sensor feedback causing the ECU to adjust
rich-lean-rich-lean every 2-3 seconds at idle (much faster at high
rpm).  If that's the case, disconnecting the sensor will stop it happening.

Check with your meter that the closed-throttle switch opens (voltage
on the line goes up to ~5 V) when you open the throttle, and closes
when the throttle is closed.  Bentley has the specs for clearance but
with a worn throttle body you may find that you have to set extra
clearance to get the switch to close when the engine is running.

Bypass the idle stab module, set basic idle speed and check timing
with it bypassed as described in Bentley.  If the throttle body is
badly worn you may not be able to set basic idle down to spec.  I
once soft-soldered a profile onto the end of the idle-adjust plug in
the throttle body so it could close farther.

All the idle stab module does is intercept the timing signal from the
distributor to the ignition driver circuit, and add increasing
advance whenever the rpm falls below the set point (750 for 49-state,
850 for California, IIRC).  So assuming it's behaving properly it
will have no effect above those speeds.  If it's causing a problem
bypassing it should tell you.

Power-steering and A/C idle switches on the 1.9l are bypass valves
that allow extra air in.  PS is from a pressure switch on the
high-pressure line.  A/C is activated by the same signal that drives
the compressor clutch.

Yrs,
d