Downloaded from www.Manualslib.com manuals search engine 7.9.7 Acceleration conditions.
During a sudden increase in throttle opening at constant
engine speed the air mass entering the manifold and combus-
tion chamber increases almost immediately due to the low
density of air, whilst the higher density fuel lags behind.
This leads to lean mixtures for a short duration if no
compensation is applied. This effect manifests itself as a
hesitation, at the onset of vehicle acceleration.
To compensate for this effect a pre-determined rate of
throttle opening is detected and the effective injection
duration is increased. This enrichment will be gradually
decreased over a number of crankshaft revolutions.
7.9.8 Deceleration lean-out conditions
While driving with the throttle in the part load region a
slight reduction in power demand (throttle opening being
reduced) will result in a momentary enrichment of the A/F
ratio. The ECU prevents this decrease in A/F by making the
injection time shorter for a limited period when detecting
the above conditions.
7.9.9 Coasting conditions.
When the throttle is closed and the engine speed is above
the coasting cut-out speed the ECU will shut the fuel supply
off to save fuel. The engine speed at which fuel is cut
off is temperature dependent to prevent engine stalling
under cold conditions.
Downloaded from www.Manualslib.com manuals search engine 8 IDLE SPEED CONTROL
Idle speed is controlled by means of the IACV (Idle Air
Control Valve) mounted on the throttle body assembly. The
IACV is driven by the IACSM (Idle Air Control Stepper Motor)
which is controlled by the ECU.
The IACV maintains constant idle speed (temperature depend-
ent) under all engine loads.
The ECU makes use of closed loop control algorithms to
ensure the best idle conditions for warm and cold engines.
Whenever the ignition is first switched the ECU selects a
pre-set idle position which is temperature dependent, there-
after it operates in the closed loop control mode.
Idle speed control is only possible with the throttle in the
closed position.
Timing advance support is utilised in the idle range to
enhance idle speed control. Spark timing is advanced by up
to 10ø if the idle speed drops below the set point, result-
ing in increased engine torque to offset the drop in speed.
If the idle speed rises above the set point the timing will
be retarded up to 10ø to reduce engine torque.
Correct idle speed control is not possible when the battery
voltage is below 9 volt.
