Fiat 1996 Brava Service Manual page 263

Engine Bravo- Brava igiuev
Fuel system 98 range
10.
MANAGEMENT OF THE ENGINE IDLE SPEED
The general objective of this strategy is to keep the engine speed around the value memorized (engine
warm: 800 [rpm]) the position assumed by the butterfly depends on the engine speed and the vehicle
speed.
- Starting.
When the key is inserted, the butterfly assumes a position which depends on the temperature of the en­
gine and the battery voltage (open-loop position).
- Engine running and accelerator pedal released.
The engine speed varies according to the temperature of the engine and is kept constant close to this
value by altering the position of the butterfly to compensate for any fluctuations in the speed.
This takes place, in particular, when external loads are applied (power assisted steering, heated rear
windscreen, etc).
If the air conditioning and the fans, both managed by the control unit, are switched on and the power
assisted steering is in the end of travel position, which is signalled by a switch, the strategy manages the
butterfly in advance of the engagement of the load.
- Normal driving.
Under these circumstances, the actuator is in the open-loop position.
- Deceleration.
In deceleration conditions outside of idling, the control unit controls the position of the butterfly
through a special (dash-pot) curve, in other words it slows down the return of the butterfly towards the
closed position; this produces a reduction in the braking effect of the engine.
In addition, if the vehicle is in deceleration conditions, the information concerning its speed correlated
to the engine speed, makes it possible to manage the dash-pot effect in an optimum manner by adpating
it to the gear engaged.
MANAGEMENT OF THE ACTIVE CHARCOAL FILTER SCAVENGING
This strategy controls the position of the active charcoal filter solenoid valve in the following way:
- during starting, the solenoid valve remains closed, preventing the fuel vapours from enriching the mix­
ture;
s
- after cold starting, the solenoid valve remains closed for the entire time the engine is warmin up;
- with the engine Warm, the control unit operates the solenoid valve in duty-cycle to control the quanti­
ty of fuel vapours sent to the inlet (scavenging of the charcoal filter), according to the engine speed
and load conditions. In particular, the system alternates scavenging and non-scavenging periods: the
self-adjustment function is activated during the latter, but disabled during the scavening stage.
- in cut-off conditions, the solenoid valve remains closed.
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