Idle Control System
JustSayGo
08-25-2005, 03:22 AM
Here is how the idle control system works on 93-95 Altimas. The (IAC/ACC) Idle Air Control/Auxiliary Control valve is attached to the air intake plenum below the intake manifold. The ECM actuates the IAC/ACC with an on/off pulse signal. The longer the signal is on, the more air is allowed to flow through the IAC/ACC valve. The IAC/ACC valve operation works with the (FICD) Fast Idle Control Device solenoid.
Before diagnosing the idle control components, make sure there are no obvious vacuum leaks (broken hoses, broken gaskets etc) where they are mounted.
With the engine running, disconnect the IAC/ACC valve electrical connector and confirm that the idle drops immediately. If it does not, continue checking the idle control system.
First check the IAC/ACC valve resistance. Probe the terminals with an ohmmeter and record the resistance. It should be approximately 10 ohms. If the IAC/ACC resistance measures out of range, replace it.
Next, remove the valve and check the pintle for excessive carbon deposits. Clean it with carb spray. Also clean the housing to remove any deposits. Also check the FICD solenoid. Using jumper wires from the battery to the FICD solenoid should make a distinct click from the solenoid. If there is no sound, replace the FICD.
Remove, disassemble, and clean the IAC/ACC assembly. Replace the O-ring and use a new gasket. Don’t submerge any electrical parts.
The (ARV) Air Regulator Valve allows air to bypass into the intake when the engine is cold for fast idle. It has its own thermostat built into the regulator assembly. Make sure the passage into the manifold isn’t plugged. Blow air through the regulator passages to check for any restriction. Warm the valve up in a pan of water (above 176 degrees) and make sure that no air will leak through the valve when it is hot. If the ARV is bad, you have to buy the whole assembly with a new IAC/ACC and FICD. Put it back on the manifold and connect the wire harness.
Remove the PCV housing and valve and clean everything that may be restricted in the PCV system.
Adjust the idle speed with the screw in the IAC/ACC according to the sticker on your hood. Your engine should idle smoother with out surging or dieing.
Before diagnosing the idle control components, make sure there are no obvious vacuum leaks (broken hoses, broken gaskets etc) where they are mounted.
With the engine running, disconnect the IAC/ACC valve electrical connector and confirm that the idle drops immediately. If it does not, continue checking the idle control system.
First check the IAC/ACC valve resistance. Probe the terminals with an ohmmeter and record the resistance. It should be approximately 10 ohms. If the IAC/ACC resistance measures out of range, replace it.
Next, remove the valve and check the pintle for excessive carbon deposits. Clean it with carb spray. Also clean the housing to remove any deposits. Also check the FICD solenoid. Using jumper wires from the battery to the FICD solenoid should make a distinct click from the solenoid. If there is no sound, replace the FICD.
Remove, disassemble, and clean the IAC/ACC assembly. Replace the O-ring and use a new gasket. Don’t submerge any electrical parts.
The (ARV) Air Regulator Valve allows air to bypass into the intake when the engine is cold for fast idle. It has its own thermostat built into the regulator assembly. Make sure the passage into the manifold isn’t plugged. Blow air through the regulator passages to check for any restriction. Warm the valve up in a pan of water (above 176 degrees) and make sure that no air will leak through the valve when it is hot. If the ARV is bad, you have to buy the whole assembly with a new IAC/ACC and FICD. Put it back on the manifold and connect the wire harness.
Remove the PCV housing and valve and clean everything that may be restricted in the PCV system.
Adjust the idle speed with the screw in the IAC/ACC according to the sticker on your hood. Your engine should idle smoother with out surging or dieing.
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