The idle air control valve - or idle control valve - adjusts the engine's idling speed. This is controlled by the engine computer. Sometimes some parts malfunction resulting in the car idling strangely or stalling. This article will show you how to check the idle valve.
Steps
Method 1 of 4: General Motors
Step 1. Check if the "Check Engine" light is on
If yes, use an OBD II scanner to retrieve the codes if the car is from 1996 or later.
If the codes are between P505 and P509, you have a problem with the idle system which could be due to the control valve (IAC)
Step 2. Older cars may have a code that can only be recovered with an original OBD scanner
Code 11 indicates the same problem as new machines and the diagnosis procedure is the same.
Step 3. Disconnect the IAC valve and turn on the machine
At this point the idle speed should increase as expected.
Step 4. Turn off the machine and reconnect the IAC valve
Restart the engine and the idle speed should return to normal. If it does, this MAY rule out the IAC but further testing will be needed. If the cost of a new valve is prohibitive, try finding one in a scrap yard and see if there is any difference.
Step 5. Use a phase finder if the idle speed does not work as expected
Connect it to the air control solenoid and look at the instrument.
The detector will flash or become dimmer for the four circuits if the problem is with the valve. Otherwise it means that the problem is related to the PCM (powertrain control module)
Method 2 of 4: Ford
Step 1. See if the "Check Engine" light is on
If so, use an OBD II scanner to retrieve the codes if the car is from 1996 or later. As with General Motors, if the codes are P505 to P509, you have a problem with the idle system.
If your car is older than '96, you will need a regular OBD scanner. You may get codes 12, 13, 16, 17, or 19, which indicate that the minimum is wrong. Sometimes codes 47 or 48 appear, indicating an air leak
Step 2. Turn off the machine and disconnect the IAC solenoid if you get any of the above codes
Step 3. Restart the engine and check if the RPM has decreased
If there are no changes, the problem is with the solenoid.
Step 4. Use an ohm reader to check the solenoid by hooking the positive lead to the VPWR and the negative to the IAC
The resistance value should be between 7.0 ohms and 13.0 ohms. If you are out of these values then the IAC solenoid is malfunctioning
Method 3 of 4: Chrysler
Step 1. Use a scanner (OBD for older 1996 vehicles or OBD II for newer vehicles) to retrieve the codes if the Check Engine Light is on
Code 25 in older cars or P505 to P509 for newer models indicates a problem with the idle system
Step 2. Use a bidirectional scanner to check idle speed by sending commands
If the motor does not respond to commands then there is a problem with the IAC solenoid, wiring or driving circuit.
Method 4 of 4: Other brands
Step 1. Check your car's manual for specific instructions
The process should be similar to those described above, but there may be additional steps or a combination of methods.
