Fiat Bravo Service Manual page 183

Engine
Fuel system
10.
Air flow graph step no.
Motor strategy
The number of working steps is dependent upon engine conditions:
- Start-up stage
When the key is inserted, the ECU controls step motor position according to engine coolant tempera-
ture and battery voltage.
- Warming-up stage
Rpm levels are corrected according to engine coolan temperature.
- With engine warm:
Idle control is dependent on a signal from the rpm sensor. When external users are activated, the E C U
governs sustained idle.
- Over-run:
The ECU recognises over-run status frofiTthe throttle potentiometer position.
It controls step motor position by means of the idle flow law (DASH - POT laws). In other words, it slows
the return of pluger (3) to its seat so that a quantity of air by-passing hole (2) reaches the engine and re-
duces levels of pollutants in the exhaust gas.
Recovery
Actuator operation disenabled and self-adaption of idling fuel mixture level blocked.
Removing-refitting engine idle control actuator (step motor)
- disconnect battery negative terminal;
- unscrew both retaining screws and withdraw the actuator;
- check condition of thoroid seal and remove any impurities from the case seat;
- refit the actuator, checking that the plunger fits easily without forcing. To do this, fit the actuator and
replace screws but do not tighten. Operate the step motor using a Fiat-Lancia/Tester until it has
moved through its entire travel. Tighten screws only after checking plunger is correctly aligned in its
seat and electrical connector is positioned correctly.
NOTE It is advisable to leave the battery negative terminal disconnected for about 20 minutes. Provid-
ed the abo ve procedure is carried out as described, the ECU will position the idle speed actuator
correctly the first time the engine is started up.
Fit new step motor retaining screws whenever they are loosened or removed because the
threads are covered with a light layer of loctyte, which guaranteeds a seal only once.
Tightening torque of step motor screws 0.36 - 0.44 da Nm.
36
The electric step motor features extremely high
accuracy and resolution (about 20 rpm). Pulses
sent from the E C U to the engine are converted
from rotary motion into straight-line
(about 0.04 mm/step) through a worm and
screw mechanism. This operates a plunger which
in turn moves to alter the by-pass duct cross-sec-
tion.
The constant idle air flow Qo arises as a result of
leakage through the butterfly valve. This is regu-
lated during production and protected by a cap.
Maximum flow Q2 arises when the plunger is ful-
ly retracted (about 200 steps corresponding to 8
mm). Between these two levels, air flow follows
the graph shown alongside.
P4A36CJ01
Bravo-Brava
Publication
@ | i 6 v
motion
no. 506.670