Chrysler RG Voyager. Manual — part 979
IDLE AIR CONTROL MOTOR
DESCRIPTION
The idle air control valve is mounted on the throt-
tle body. The PCM operates the idle air control valve
(Fig. 15) or (Fig. 16).
OPERATION
The PCM adjusts engine idle speed through the
idle air control valve to compensate for engine load,
coolant temperature or barometric pressure changes.
The throttle body has an air bypass passage that
provides air for the engine during closed throttle idle.
The idle air control valve regulates air flow through
the bypass passage.
The PCM controls engine idle speed by adjusting
the position of the idle air control valve. The adjust-
ments are based on inputs the PCM receives. The
inputs are from the throttle position sensor, crank-
shaft position sensor, coolant temperature sensor,
MAP sensor, vehicle speed sensor and various switch
operations (brake, park/neutral, air conditioning).
When engine rpm is above idle speed, the IAC is
used for the following functions:
• Off-idle dashpot
• Deceleration air flow control
• A/C compressor load control (also opens the pas-
sage slightly before the compressor is engaged so
that the engine rpm does not dip down when the
compressor engages)
Target Idle
Target idle is determined by the following inputs:
• Gear position
• ECT Sensor
• Battery voltage
• Ambient/Battery Temperature Sensor
• VSS
• TPS
• MAP Sensor
REMOVAL
When servicing throttle body components, always
reassemble components with new O-rings and seals
where applicable. If assembly of component is diffi-
cult, a light coat of engine oil may be applied to the
O-RINGS ONLY to aid assembly. Use care when
removing hoses to prevent damage to hose or hose
nipple.
(1) Disconnect negative cable from battery.
(2) Remove electrical connector from idle air con-
trol valve (Fig. 17).
(3) Remove idle air control valve mounting screw.
(4) Remove valve from throttle body. Ensure the
O-rings is removed with the valve.
INSTALLATION
When servicing throttle body components, always
reassemble components with new O-rings and seals
where applicable. If assembly of component is diffi-
cult, a light coat of engine oil may be applied to
the O-RINGS ONLY (Fig. 18) to aid assembly. Use
care when removing hoses to prevent damage to hose
or hose nipple.
(1) Carefully place idle air control motor into
throttle body.
Fig. 15 TPS/IAC 2.4L
1 - Idle Air Control Valve
2 - Throttle Position Sensor
Fig. 16 TPS/IAC 3.3/3.8L
1 - Idle Air Control Valve
2 - Throttle Position Sensor
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FUEL INJECTION
14 - 33
(2) Install mounting screw. Tighten screw to 7 N·m
(62 in. lbs.) torque.
(3) Connect electrical connector to idle air control
motor.
(4) Connect negative cable to battery.
INLET AIR TEMPERATURE
SENSOR
DESCRIPTION
The IAT Sensor is a Negative Temperature Coeffi-
cient (NTC) Sensor that provides information to the
PCM regarding the temperature of the air entering
the intake manifold (Fig. 19).
MAP SENSOR
DESCRIPTION
The MAP sensor (Fig. 20) or (Fig. 21) mounts to
the intake manifold. The sensor is connects electri-
cally to the PCM.
OPERATION
The MAP serves as a PCM input, using a silicon
based sensing unit, to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When MAP equals Barometric pressure, the pulse
width will be at maximum.
Fig. 17 IDLE AIR CONTROL VALVE LOCATION
Fig. 18 O-RINGS
1 - O-rings
Fig. 19 3.3/3.8L IAT SENSOR
Fig. 20 MAP SENSOR - 2.4L
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FUEL INJECTION
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IDLE AIR CONTROL MOTOR (Continued)
Also like the cam and crank sensors, a 5 volt ref-
erence is supplied from the PCM and returns a volt-
age
signal
to
the
PCM
that
reflects
manifold
pressure. The zero pressure reading is 0.5V and full
scale is 4.5V. For a pressure swing of 0 — 15 psi the
voltage changes 4.0V. The sensor is supplied a regu-
lated 4.8 to 5.1 volts to operate the sensor. Like the
cam and crank sensors ground is provided through
the sensor return circuit.
The MAP sensor input is the number one contrib-
utor to pulse width. The most important function of
the MAP sensor is to determine barometric pressure.
The PCM needs to know if the vehicle is at sea level
or is it in Denver at 5000 feet above sea level,
because the air density changes with altitude. It will
also help to correct for varying weather conditions. If
a hurricane was coming through the pressure would
be very, very low or there could be a real fair
weather, high pressure area. This is important
because as air pressure changes the barometric pres-
sure changes. Barometric pressure and altitude have
a direct inverse correlation, as altitude goes up baro-
metric goes down. The first thing that happens as
the key is rolled on, before reaching the crank posi-
tion, the PCM powers up, comes around and looks at
the MAP voltage, and based upon the voltage it sees,
it knows the current barometric pressure relative to
altitude. Once the engine starts, the PCM looks at
the voltage again, continuously every 12 milliseconds,
and compares the current voltage to what it was at
key on. The difference between current and what it
was at key on is manifold vacuum.
During key On (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring known good sensor in
you work area.
As the altitude increases the air becomes thinner
(less oxygen). If a vehicle is started and driven to a
very different altitude than where it was at key On
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open throttle, based upon
TPS angle and RPM it will update barometric pres-
sure in the MAP memory cell. With periodic updates,
the PCM can make its calculations more effectively.
The PCM uses the MAP sensor to aid in calculat-
ing the following:
• Barometric pressure
• Engine load
• Manifold pressure
• Injector pulse-width
• Spark-advance programs
• Shift-point strategies (F4AC1 transmissions
only, via the PCI bus)
• Idle speed
• Decel fuel shutoff
The PCM recognizes a decrease in manifold pres-
sure by monitoring a decrease in voltage from the
reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; as pressure
changes, voltage changes proportionately. The range
of voltage output from the sensor is usually between
4.6 volts at sea level to as low as 0.3 volts at 26 in. of
Hg. Barometric pressure is the pressure exerted by
the atmosphere upon an object. At sea level on a
standard day, no storm, barometric pressure is 29.92
in Hg. For every 100 feet of altitude barometric pres-
sure drops .10 in. Hg. If a storm goes through it can
either add, high pressure, or decrease, low pressure,
from what should be present for that altitude. You
should make a habit of knowing what the average
pressure and corresponding barometric pressure is
for your area.
REMOVAL
REMOVAL - 2.4L
(1) Disconnect the negative battery cable.
(2) Disconnect electrical connector and vacuum
hose from MAP sensor (Fig. 20).
(3) Remove two screws holding sensor to the
intake manifold.
REMOVAL - 3.3/3.8L
(1) Disconnect the negative battery cable.
(2) Remove vacuum hose and mounting screws
from manifold absolute pressure (MAP) sensor (Fig.
21).
(3) Disconnect electrical connector from sensor.
Remove sensor.
Fig. 21 MAP SENSOR - 3.3/3.8L
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MAP SENSOR (Continued)
INSTALLATION
INSTALLATION - 2.4L
(1) Install sensor.
(2) Install two screws and tighten.
(3) Connect the electrical connector and vacuum
hose to the MAP sensor (Fig. 20).
(4) Connect the negative battery cable.
INSTALLATION - 3.3/3.8L
(1) Install sensor (Fig. 21).
(2) Install screws and tighten to PLASTIC MAN-
IFOLD 1.7 N·m (15 in. lbs.) ALUMINUM MANI-
FOLD 3.3 N·m (30 in. lbs.) .
(3) Connect the electrical connector to the sensor.
Install vacuum hose.
(4) Connect the negative battery cable.
O2 SENSOR
DESCRIPTION
The upstream oxygen sensor threads into the out-
let flange of the exhaust manifold (Fig. 22) or (Fig.
23).
The downstream heated oxygen sensor threads into
the outlet pipe at the rear of the catalytic convertor
(Fig. 24).
OPERATION
A seperate upstream and downstream grounds are
used on the NGC vehicles (4 Cyl.).
As vehicles accumulate mileage, the catalytic con-
vertor deteriorates. The deterioration results in a
less efficient catalyst. To monitor catalytic convertor
deterioration, the fuel injection system uses two
heated oxygen sensors. One sensor upstream of the
catalytic convertor, one downstream of the convertor.
The PCM compares the reading from the sensors to
calculate the catalytic convertor oxygen storage
capacity and converter efficiency. Also, the PCM uses
the upstream heated oxygen sensor input when
adjusting injector pulse width.
When the catalytic converter efficiency drops below
emission standards, the PCM stores a diagnostic
trouble code and illuminates the malfunction indica-
tor lamp (MIL).
The O2 sensors produce a constant 2.5 volts on
NGC vehicles, depending upon the oxygen content of
the exhaust gas. When a large amount of oxygen is
Fig. 22 O2 SENSOR UPSTREAM 1/1 - 2.4L
Fig. 23 O2 SENSOR UPSTREAM 1/1 - 3.3/3.8L
Fig. 24 O2 SENSOR DOWNSTREAM 1/2 - 2.4/3.3/
3.8L
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FUEL INJECTION
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MAP SENSOR (Continued)
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