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Date:         Mon, 17 Sep 2012 16:26:16 -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 stabilizer question--1.9
Comments: To: Larry Alofs <lalofs@GMAIL.COM>
In-Reply-To:  <CA+r=Jhp1J38EAD2p3e3m0fxQ_dwFMegkzbiO2nMoQGSr8bmkyA@mail.g
              mail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 04:46 PM 9/16/2012, Larry Alofs wrote: >Does an idle stabilizer contain some type of tachometer? I understand >that it adjusts the idle speed by adjusting the ignition timing >slightly. Does it watch the time interval between between ignition >pulses and use some absolute standard to decide if the idle is too >fast or too slow?

Yes, it believes in either 700 or 750 rpm as the standard idle speed (750 for the California versions). As long as the distributor pulses come in faster than that it does nothing at all. When they slow down, it starts sending them early (advancing the timing).

You're supposed to set your idle to the nominal speed by adjusting the bypass plug in the throttle body; with everything up to temperature, battery charged and no loads operating (and the idle stab module bypassed). Once that's set and the idle stab is back in circuit, it will advance timing to compensate for charging loads and such. Power steering and A/C put bigger loads on the system than this approach can handle, so each of them has an air-bypass valve that opens when either of those systems is loaded, and allows extra air into the intake.

The 2.1l system has the same effect, but it does it by adding bypass air via a solenoid valve with a fancy control system. It has plenty of range, so the A/C and P/S systems work through it rather than having separate arrangements.

Neither system can lower the idle, only raise it.

Yours, David


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