Fiat 1996 Brava Service Manual page 449

Bravo- Brava 0>
1998 range
16v
Engine
Fuel system
10.
8,9 mm
Qi
Qo
200 220
The step motor is very precise and offers high
resolution (about 220 steps per second).
Pulses sent by the electronic control unit to
the engine are converted from rotary motion
into linear movement (about 0.04 mm/step)
via a worm screw mechanism. The plunger
then works to alter the cross section of the by
pass port.
The constant minimum air flow (Qo) due to
air leaking beneath the throttle valve is ad­
justed during production and ensured by a
tamperproof cap. Maximum air flow (Q2) oc­
curs when the plunger is fully retracted (about
220 steps corresponding to 8.9 mm).
Air flow follows the law shown in the graph
alongside for intermediate values.
Motor strategy
The number of working steps depends on engine condition:
- Ignition stage
When the ignition key is inserted, the control unit makes the step motor take up a position dependent
upon coolant temperature and battery voltage.
- Warm-up stage
RPM is adjusted according to coolant temperature
- With engine warm:
Idle management depends on a signal from the engine rpm sensor. The control unit manages sustained
idle mode when external loads are activated.
- During deceleration
The electronic control unit identifies deceleration stage from throttle potentiometer position.
It controls step motor position via the idle flow law (dashpot law), i.e. it slows the return of plunger (3)
to its seat so that a quantity of air bypassed from hole (2) reaches the motor and reduces levels of pol­
lutants in exhaust gases.
Recovery
Actuator operation disabled, fuel vapour recirculation self-adaptation inhibited and speed limited to 1200
rpm.
Removing-refitting engine idle speed actuator (step motor)
Procedure for premodification cars
- disconnect the battery negative terminal.
- unscrew both retaining bolts and withdraw the actuator;
- check the condition of the o-ring and remove any impurities from the seat in the case;
- refit the actuator and check that the plunger fits properly into its seat without forrcing.
Step motor bolt tightening torque 0.35 -
0.45da N m
NOTE The engine idle speed actuator is built
into the throttle body in postmodifi-
cation cars.
Connector wiring
The numbers in squares indicate the control
unit pins.
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