54 Technical Description
Idle speed control
0
49
When the accelerator pedal is not activated and the
throttle is closed, the engine receives air only via the
idle air control valve.
The ECM controls the degree of opening in the valve
to keep idling speed constant. This means for exam-
ple that the valve opens slightly more when the A/C
compressor is switched on or if DRIVE has been se-
lected, in order to compensate the idling speed,
which would otherwise fall.
The idle air control valve
1
which has a single coil, is
supplied with current from the main relay. The valve
is controlled by a 500 Hz PWM signal from pin 49 of
the control module. The longer the control module
keeps pin 49 grounded, the wider the valve opens.
The control module is programmed to maintain en-
gine idling speed at 850
± 50 rpm. Rapid changes in
idling speed cannot be compensated for by changing
the flow of ai_r. Instead, ignition timing at idling speed
is so arranged that engine speed is maintained at a
constant level.
If there is an open circuit to the ~dte air control valve,
the opening in the valve is set by a spring so that the
idling speed is at least 1000 rpm when the engine is
warmed up.
Saab 9000
+30
230
272
589
µp
-------CJ)
~
,..._
i
~
To Next Page
Loading...
