BOMBARDIER Johnson 90 Service Manual page 80

ENGINE CONTROL SYSTEM
ELECTRONIC FUEL INJECTION SYSTEM
Bypass AIR SCREW / PASSAGE
Since the throttle valva is almost fully closed when idlíng /
trollíng, the main flow of air necessary to rnaintain idling / troll­
ing speed passes through the bypass air passage. The
bypass air screw controls the flow of air through the passage
and provides a rneans of partially adjusting the total amount of
air necessary for idling / trolling.
NOTE:
See page 2-15 for the bypass air screw adjustment
proce­
dure.
IAC VALVE / PASSAGE
The IAC valve is a linear solenoid plunger type rnounted on
the intake manifold. lts purpose is to control the amount of
intake air flowing from the IAC passage. The IAC valve is
driven by the duty cycle signal from the ECM.
ldle Air Control System
OUTLINE
The ECM controls the duty cycle signal of the IAC valve to regulate a portian of the intake air flow to the
intake manifold. This system is used for the following purposes:
• To keep idling / trolling at specified speed.
• To improve drive ability when deceleratíng. (Oashpot effect)
• To improve engine starting and warm-up performance. {Fast-idle function)
The sensors / switch shown below monitor current engine condition and send signals to the ECM. Based
on these signals, the ECM determines the optimum duty cycle (repeating "ON" time rate within a cycle).
A repeating ON / OFF signal at a specified rate (250 times a second) is then sent to the IAC valve.
CKP sensor:
lnforms ECM of engine speed.
MAP sensor:
lnforms ECM of intake manifold pressure.
ECM
CTP switch:
lnforms ECM of throttle position (open/closed).
Cylinder temp. sensor:
lnforms ECM of cylinder temperatura.
Signal
IAC valve
3-20