Engine Management
Electronic Throttle
The electronic throttle enables the ECM to
perform the following functions:
engine air flow (ie. power) control
engine idle speed control
vehicle cruise control
stability/traction control (in response to
ABS commands)
engine power limiting
vehicle speed limiting
reverse gear torque reduction
Engine Air Flow Control
During normal operation, when the accelerator
pedal is above idle, the ECM positions the
throttle valve in response to the inputs from the
accelerator pedal position sensor. The throttle
valve follows or leads at a minimum distance the
mechanical guard as the guard is moved by the
accelerator pedal. Thus engine power output is
directly related to driver demand. With the
engine running, the time for the throttle to travel
from idle to fully open is approximately 120 ms
maximum, and from fully open to idle
approximately 140 ms maximum.
Idle Speed Control
During engine idle speed control, the ECM
operates in a closed speed control loop to
maintain a given target idle speed. The ECM
uses gear selection, intake air temperature and
battery voltage to determine the required target
idle speed.
Gear selection is derived from the input of the
Park/Neutral switch in the transmission rotary
Battery voltage is monitored and, if low voltage is
detected (11.8 V and below), target idle speeds
are increased by up to 50 rpm to increase the
output from the generator.
When the ECM selects a change of target idle
speed, overshoot is kept to 50 rpm maximum.
Certain vehicle services/functions cause a
significant change in engine load as they are
selected on and off. To minimize the effect on
idle speed, the ECM anticipates the change in
load rather than correct the subsequent change in
rpm. The services/functions the ECM anticipates
load changes for are:
A/C compressor clutch
gear shifts between Park/Neutral and
headlamps and side lamps
windshield and backlight heaters
radiator cooling fans.
The ECM detects gear shifts, headlamp status
and side lamp status from their related status
messages on the CAN data bus. The ECM
directly controls the A/C compressor clutch and
the radiator cooling fans. The windshield and
backlight heaters are controlled by the ACCM
upon consent of the ECM via the heater
request/load inhibit circuits.
If a fault develops in the idle control function, the
ECM goes to open loop control. During open loop
control, rpm is within +100 and -0 rpm of the
target speed for a warm engine (ie. when the
coolant temperature is >30 ˚C (86˚F).
Idle Target Speeds
Intake Air Temperature, ˚C (˚F) Engine Speed, (rpm)
Drive/Reverse Park/Neutral
>-10 (14) 600 ± 25 650 ± 25
-10 to >-20 (14 to >-4) 625 ± 25 675 ± 25
-20 to >-30 (-4 to >-22) 650 ± 25 700 ± 25
-30 (-22) 675 ± 25 725 ± 25
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