Acura RL (1996-2004 year). Manual — part 386
Idle Control System
NOTE: If DTC P1508 is stored at the same time as DTC P0505, troubleshoot DTC P1508 first, then troubleshoot DTC P0505.
Possible Cause
• IAC valve mechanical malfunction
• Idle air control thermal valve malfunction
• Throttle body clogged port, improper adjustment
• Intake manifold gasket leakage
• Intake air hose loose or leaking
• Vacuum hoses leakage
• ECT sensor incorrect output
• Throttle Position sensor incorrect output*
•: '96 model only
— The MIL has been reported on.
— DTC P0505 is stored.
Problem verification:
1. Start the engine. Hold the
engine at 3,000 rpm with no
load (in Park or neutral) until
the radiator fan comes on,
then let it idle.
2. With the scan tool, check the
following items ('96 model
only).
— Throttle position should be
about 10% with the throttle
fully closed.
— Engine coolant tempera-
ture should be about 176 -
194°F (80-90°C).
If they are not within the spec.,
repair the faulty sensor circuit.
3 Check the engine speed at
idle with no-load conditions:
headlights, blower fan, rear
defogger, radiator fan, and air
conditioner are not operating.
Is it 650 50 rpm?
NO
Is it 600 rpm or less?
YES
Intermittent failure, system is OK
at this time.
NO
) (To page
YES
The scan tool indicates Diagnostic Trouble Code (DTC) P0505: Idle control system malfunction.
Troubleshooting Flowchart
Main Menu
Table of Contents
Idle Control System
Idle Control System (cont'd)
Check the IAC valve:
Disconnect the 2P connector from
the IAC valve.
Does the engine speed drop
or the engine stall?
Replace the IAC valve.
YES
Adjust the (base) idle speed (see
page
). If it's impossible,
dean the ports in the throttle body.
IDLE AIR
CONTROL
THERMAL
VALVE
Check the idle air control thermal
valve:
1. Turn the ignition switch OFF.
2. Remove the cover from the
idle air control thermal valve.
3. Start the engine and let it idle.
4. Put your finger on the valve
seat area and check for air
flow.
Is air flow felt in the valve
seat area?
NO
Check engine coolant level and
for air in the cooling system. If
OK, replace the idle air control
thermal valve.
Check for vacuum leaks, make
sure the throttle valve is com-
pletely closed, and repair as
necessary.
Adjust the idle speed (see
page
). If it's impossi-
ble, replace the IAC valve.
NOTE: If the cover of the idle air
control thermal valve was
removed, do the PCM reset pro-
cedure.
YES
NO
VALVE
SEAT
AREA
Main Menu
Table of Contents
— The MIL has been reported on.
— DTC P1508 is stored.
Problem verification:
1. Do the PCM Reset Procedure.
2. Start the engine.
Is DTC P1508 indicated?
YES
Check for an open in the wire
(IGP1 line):
1. Turn the ignition switch OFF.
2. Disconnect the IAC valve con-
nector.
3. Turn the ignition switch ON (II).
4. Measure voltage between body
ground and the IAC valve con-
nector terminal No. 2.
Is there battery voltage?
Is there battery voltage?
YES
Check the IAC valve function:
Momentarily connect PCM con-
nector terminals A5 and A12 with
a jumper wire several times.
Does the IAC valve click?
YES
Substitute a known-good PCM
and recheck (see page
for
immobilizer information). If symp-
tom/indication goes away, replace
the original PCM.
SHAFT
Intermittent failure, system is OK
at this time. Check for poor con-
nections or loose wires at C253
(located at left shock tower),
C129 (IAC valve) and PCM.
SPRING
IAC VALVE CONNECTOR (C129)
Repair open in the wire between
IAC valve and PGM-FI main relay.
Wire side of female terminals
PCM CONNECTOR A (26P)
Repair open or short in the wire
between PCM (A5) and IAC valve.
Wire side of female terminals
JUMPER WIRE
Replace the IAC valve.
NO
NO
Check for an open or short in the
wire (IACV line):
1. Turn the ignition switch OFF
and reconnect the IAC valve
connector.
2. Disconnect the PCM connec-
tor A (26P).
3. Turn the ignition switch ON (II).
4. Measure voltage between
body ground and PCM con-
nector terminal A5.
NO
YES
VALVE
To INTAKE
MANIFOLD
From AIR
CLEANER
COIL
NO
Idle Air Control (IAC) Valve
The scan tool indicates Diagnostic Trouble Code (DTC) P1508: A problem in the Idle Air Control (IAC) valve
circuit.
The IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from the PCM in
order to maintain the proper idle speed.
Main Menu
Table of Contents
Idle Control System
Air Conditioning Signal
This signals the PCM when there is a demand for cooling from the air conditioning system.
Inspection of Air Conditioning
Signal.
PCM CONNECTORS
Check for a short in the wire
(ACS line):
1. Turn the ignition switch OFF.
2. Disconnect the radiator fan
control unit 12P connector.
3. Turn the ignition switch ON (II).
4. Measure voltage between
PCM connector terminals C2
and A26.
Wire side of female terminals
Is there battery voltage?
NO
YES
Check for an open in the wire
(ACC line):
1. Turn the ignition switch OFF.
2. Reconnect the radiator fan
control unit 12P connector.
3. Turn the ignition switch ON (II).
4. Momentarily connect PCM
connector terminals A8 and
A26 with a jumper wire sever-
al times.
ACS (PNK)
YES
Repair short in the wire between
the PCM (C2) and the radiator
fan control unit.
PCM CONNECTOR A (26P)
Wire side of female
terminals
— Substitute a known-good PCM
for immobilizer information).
If prescribed voltage is now
available, replace the original
PCM.
— See the air conditioner inspec-
Is there continuity?
NO
Check for a short in the wire (ACS
line):
1. Turn the ignition switch OFF.
2. Disconnect the PCM connec-
tor C (12P).
3. Check for continuity between
body ground and PCM con-
nector terminal C2.
Main Menu
Table of Contents
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