Idle
 

'91 STD with A/C shut off.

What controls the idle from veering off its mark? Keeping it on the money
and not moving a fraction.

idle air bypass which is basically an orifice conected between the front of
the the throttle bypasisng the throttle body and connected to the intake
manifolod which is controlled by a stepper motor openning and closing the
roifice openning when throttle is closed and closing when throttle is open
the motor is controled by the PCM (engine computer) which has throttle and
air flow readinjgs.

"Gary" > wrote in message
news:PMJYe.7204$iu5.7084@trndny04...
> '91 STD with A/C shut off.
>
> What controls the idle from veering off its mark? Keeping it on the money
> and not moving a fraction.
>
>

There are two conditions that you need to know about.
Open loop (Tens pin shorted to ground)
Closed loop (Normal)
The open loop mode is used to set base timing and idle.
Closed loop allow the computer to control the idle.

If you are adjusting the idle with the air bleed screw, open loop (on NB's)
should be above closed loop by 1 to 2 hundred RPM, or no less than the
closed loop idle speed. Idle hunting in closed loop usually indicates that
one of the sensor outputs is not as it should be. (Assuming that the engine
is actually in tune, with good plugs wires, etc.)
Sometimes the idle air valve controlled by the computer sticks, due to
varnish, and will cause the computer to step it beyond the correct setting.

"Gary" > wrote in message
news:PMJYe.7204$iu5.7084@trndny04...
> '91 STD with A/C shut off.
>
> What controls the idle from veering off its mark? Keeping it on the money
> and not moving a fraction.
>
>