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Date:         Sat, 20 Jul 2013 22:21:39 -0700
Reply-To:     Craig Forney <craig@OPUS.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Craig Forney <craig@OPUS.COM>
Subject:      Re: Idle Control Issues
In-Reply-To:  <CAKBXc7ePWnf04mK6MR47DAvg3YkreoVOC59O4iOzh+-H24mwpA@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

A couple more ISCM and IAC points:

The AC compressor engaging sends a signal to the ISCM and increases idle speed a bit when the throttle is closed (assuming the throttle position switch is actually closed). When you step on the gas, it increases the flow even more so that the engine doesn't stumble. If the TPS is not giving a closed throttle signal to the ISCM, the idle speed will jump up typically to 1500-2000 RPM. Sometimes "blipping" the gas pedal will bump the TPS switch enough to reduce the idle towards 880 RPM. This sounds like Casey's problem. It appears the IAC is working just fine, as it has no problem increasing the idle speed.

Craig in Cupertino 1987 Syncro GL 1987 Syncro Westy

> On Jul 20, 2013 9:54 PM, "Craig Forney" <ccforney@gmail.com> wrote: > > > > I have spent a lot of time with Vanagon Idle Stabilation Control Modules (ISCMs) and thought it might to explain the workings to help those with idle problems diagnose and fix them. > > > > Under certain conditions, the ISCM (installed behind the right, rear taillight) adds additional air into the intake plenum, bypassing the throttle body. This increases the engine RPMs to compensate for the engine being cold, air conditioning, power steering and some other conditions needing additional power. > > > > These functions are in addition to trying to maintain an idle of about 880 RPM. If the idle dips below 880 the air flow past the throttle body is increased to provide a stable idle. > > > > The additional air to the intake plenum is regulated by the Idle Air Control (IAC) Valve (cylindrical object on top of the engine). It is controlled with a pulse width modulated (PWM) 5 volt signal (from the ISCM) that is going from 0 to 5 volts and back to 0 volts about 8.6 times every 1/1000 of a second, basically opening and closing the valve each 0-5v transition. The duration of the 5 volt signal determines how much time the valve is open and how much air is getting redirected. > > > > When working properly wirh a good ISCM, the IAC should hum when the key is on. > > On Jul 20, 2013 12:36 PM, "Zeitgeist" <gruengeist@gmail.com> wrote: > > > > > > So, I just got back from a quick hop to the local Quickee Mart, and I > > > decided to experiment a little. I dialed down the AC temp switch which > > > cycles the compressor on and off a lot more. The idle issues would appear > > > and then disappear with the compressor, which seems to be more of a relay > > > issue than something with the valve--no? > > > > > > On an unrelated topic, my rear main is really leaking badly and dripping > > > onto my exhaust. Since these things ignite with alarming ease, am I > > > tempting the gods by limping along like this for longer than I should? > > > That's obviously a rhetorical question, 'cause just driving a van tempts > > > the gods. > > > > > > > > > > > > > > > -- > > > Casey


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