Intake Throttle Control - Isuzu 4HL1 Workshop Manual

1A-6 Engine Control System

Intake Throttle Control

Legend
1. Intake throttle valve
2. ITP (intake throttle position) sensor
The intake throttle control system changes (throttles)
the air according to the vehicle status and reduces
suction noises generated from the working exhaust
brake and acceleration. This control is made by
opening and closing the intake throttle valve. The
intake throttle valve is operated by the DC motor and
changing the drive voltage (duty: see Note 1) opens
and closes the valve. The intake throttle valve is fully
opened in the normal state (i.e., the DC motor is
inactive) and gradually reduces the opening as the
drive voltage is increased. The ECM uses the ITP
(intake throttle position) sensor to detect the working
condition of the intake throttle valve. When the valve
opening gets smaller (the drive voltage is increased),
the output voltage of the ITP sensor becomes lower.
The valve position is normally calculated using engine
coolant temperature, engine speed, and desired
injection quantity, and the DC motor drive voltage is
determined from this calculated value. However, the
ECM completely opens the throttle valve when the
vehicle is in idle stop, DTC is set for the intake throttle
system, AP sensor system, or EGR system, gear
shifting is performed (for manual transmission vehicle),
the engine coolant temperature is low (less than 70°C),
or the vehicle is in startup or engine stall status while it
completely closes the valve immediately after the key
1
3
2
3. Intake throttle DC motor
switch is turned off (within 0.5 to 3.0 seconds).
There is an opposing relationship between intake
throttle control and EGR control. When the intake
throttle valve is opened, the EGR valve is closed, and
vice versa.
Note 1: Duty (%) = Energize ratio
LNW21AMF005701