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