Date:         Sat, 12 Jan 2002 11:45:01 -0600
Reply-To:     John Clavin <jc@AUSTIN.RR.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Clavin <jc@AUSTIN.RR.COM>
Subject:      Re: Idle stabilizer
In-Reply-To:  <200201100506.g0A56unc023699@txmx01.mgw.rr.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Per the wiring diagrams in Bentley and my own observations on my 1985
Vanagon, the idle stabilizer is connected only between the Hall sender in
the distributor and the Hall control unit mounted on an aluminum plate on
the side wall next to the idle stabilizer. Three wires connect the Hall
sender to the Control unit. It is these three wires that are routed through
the two plugs on the idle stabilizer.

Having hacksawed open my defunct idle stabilizer, I found a moderately
complex circuit board with several integrated circuits (IC). Tracking down
the part numbers (MC14538) on some of these ICs revealed them to be
monostable multivibrator circuits. The others were all basic logic gates.

Typically, multivibrator circuits are used to create free-running or
triggered oscillators. My guess is that in the idle stabilizer they are
triggered by the sender unit to send the actual ignition pulses to the Hall
Control unit. The reason for this would be to provide some signal
conditioning that evens out the timing between individual, erratic pulses
from the sender. It also would provide some wave form shaping of the pulses
so as to make them more uniform, and hence more reliable, as seen by the
Hall Control unit. The net effect would be to take a jittery stream of
poorly shaped pulses and replace it with a more uniform stream of evenly
shaped and spaced pulses.

Disconnecting the idle stabilizer by connecting the cables to it together
merely sends the raw sender signal to the Hall Control unit. If the
electrical signal from the sender is "clean" because the sender produces a
good signal and the engine is running smoothly, then it is likely that you
can run without the stabilizer.

An examination of the circuit board reveals that the three wires involved
are power, ground, and signal. I doubt the idle stabilizer itself knows
much about what the temp senders or O2 sensor are doing. Decisions based on
those outputs are probably performed in the ECU.

In addition to the wire from the idle stabilizer, the Hall Control Unit
connector also has wires which connect to the ignition coil and the ECU. I
suspect this control unit functions much as an electronic relay, switched
on and off by the Hall signal, and handling the higher currents involved
with the coil. The heat sink it is mounted on suggests it has some high
power transistors doing this. The wire to the ECU is probably an output
which tells the ECU what the ignition is doing, although it could be some
other type of control signal from the ECU.

If the above analysis is correct, then the idle stabilizer is always "on"
and performing its function when plugged in. I could see no way that the
ECU or Hall Control Unit could tell it to turn off for a warm engine. I
suspect that it may seem to turn off because its effects under those
running conditions are not as critical or noticeable in terms of engine
performance.

Regards.
John Clavin

At 12:00 AM 1/10/02 -0500, you wrote:
>Here's a new question for you though:
>Is the idle stabilizer only active when the idle switch is activiated?