The Idle Air Control (IAC) valve is used to control idle speed. The amount of air allowed to bypass the throttle plate is determined by the PCM.
When the engine is cold, air flows through the valve during all modes of engine operation to maintain the factory set idle speed. This will need to be tested before replacement, but it is more than likely the problem.
See Figure 1
Fig. 1: Typical IAC valve wiring schematic and connector terminal identification-1.8L engines
Turn the ignition key OFF.
Connect jumper wires from the sensor connector to the wiring harness. This permits the engine to operate normally while you check the sensor.
Connect a Digital Volt Ohmmeter (DVOM), set to read resistance, between sensor terminal SIG and the negative battery cable.
The resistance should not be greater than 10,000 ohms.
Connect the DVOM, set to read resistance, between sensor terminal VPWR and the negative battery cable.
Turn the ignition key ON.
Connect the DVOM, set to read voltage, between sensor terminal VPWR and the negative battery cable.
The voltage should be more than 1 volt.
Connect the DVOM, set to read voltage, between sensor terminal SIG and the negative battery cable.
If the readings are not within specifications, replace the IAC valve.
1.9L and 2.0L Engines
See Figures 2, 3 and 4
Fig. 2: IAC valve (solenoid) connector terminal locations-1.9L and 2.0L engines
Unplug the sensor electrical connection.
Due to the diode in the IAC valve, be sure to observe the correct polarity when connecting the DVOM.
Connect a Digital Volt Ohmmeter (DVOM), set to read resistance, between the sensor terminals as follows. Connect the positive lead to the VPWR terminal and the negative lead to the IAC terminal.
The resistance should be between 6 and 13 ohms.
Measure the resistance between either of the valve terminals and the valve body. The resistance should be greater than 10,000 ohms.
If the resistances are not within specification, replace the sensor.
Fig. 3: Connect the DVOM positive lead to the VPWR terminal and the negative lead to the IAC terminal. The resistance should be between 6 and 13 ohms
Fig. 4: Measure resistance between either of the valve terminals and the valve body. The resistance should be greater than 10,000 ohms
REMOVAL & INSTALLATION
See Figure 5
Disconnect the negative battery cable.
Remove the throttle body.
Unfasten the IAC valve retaining screws and remove the valve.
Remove and discard the valve gasket.
Fig. 5: Unfasten the IAC valve retaining screws and remove the valve-1.8L engines
Install a new valve gasket.
Install the valve and tighten its retaining screws to 25-36 inch lbs. (3-4 Nm).
Install the throttle body.
Connect the negative battery cable.
See Figure 6
If necessary on 2.0L engines, remove the air cleaner outlet tube for easier access.
Unplug the IAC valve electrical connection.
Unfasten the valve retainers, then remove the valve and gasket.
Fig. 6: Location of the IAC valve retainers-2.0L engines
Use a scraper to CAREFULLY clean the IAC valve mating surfaces.
Install a new IAC valve gasket and valve.
Install and tighten the valve retainers to 71-97 inch lbs. (8-11 Nm).
Attach the IAC valve electrical connection.
If removed, install the air cleaner outlet tube.
If you have further questions on this, please feel free to reply.
Thanks for asking!
You most likely have a vacuum leak in the system somewhere. Do a visual inspection of all of the vacuum hoses for any that may have became disconnected or rotted and replace as needed. Also check the egr valve and make sure it is not all carboned up and not fully seating, this will cause a substantial vacuum leak.
If nothing is found, you should have the computer scanned for any diagnostic codes that may have been stored in the systems memory.
A malfunctioning EGR valve can cause one or more of the following:
Rough idle or stalling on deceleration
Hesitation or surge
Abnormally low power at wide-open throttle
Before performing any test on the EGR system components, make sure the hoses are not kinked or damaged, any electrical connection are loose, corroded or damaged.
Exhaust Gas Recirculation (EGR) Valve
Fig. 1: Some EGR valves may be tested using a vacuum pump by watching for diaphragm movement
Start the car and let the engine reach normal operating temperature.
Turn the engine OFF and connect a vacuum tester (pump) to the EGR valve vacuum source port.
Turn the engine ON and idle the engine.
Slowly apply 5-10 in. Hg (16-33 kPa) of vacuum; if the engine idles roughly or stalls, the EGR valve is functioning properly.
If the engine does not idle rough replace the EGR valve.
EGR Vacuum Regulator (EVR) Solenoid
See Figure 2
Fig. 2: EVR solenoid wiring schematic
Unplug the EVR solenoid electrical connection.
Using a high impedance Digital Volt Ohmmeter (DVOM), probe the terminals of the solenoid.
The resistance should be 20-70 ohms on 1991-96 models, or 26-40 ohms on 1997-99 models.
There are two types of EVR solenoids used. One is a normally open solenoid and the other is a normally closed solenoid. Follow both testing procedures to determine which type of solenoid you are testing.
For a normally open solenoid, test it as follows:
Trace the hose that runs from the solenoid to the EGR valve and unplug the hose from the solenoid.
Using a hand pump, apply 10-15 in. Hg (33-50 kPa) of vacuum to the solenoid. The vacuum should hold.
Apply 12 volts to the solenoid and the vacuum should be released.
For a normally closed solenoid, test it as follows:
Using a hand pump, apply 10-15 in. Hg (33-50 kPa) of vacuum to the solenoid. The vacuum should not hold.
Apply 12 volts to the solenoid, then re-apply 10-15 in. Hg (33-50 kPa) of vacuum and it should hold.
If the solenoid does not meet the specifications outlined in the tests, it may be defective and must be replaced.
Pressure Feedback Electronic (PFE)/Differential Pressure Feedback Electronic (DPFE) EGR System
See Figure 3
The PFE type system is a subsonic, closed loop EGR system that controls EGR flow rate by monitoring the pressure drop across a remotely located sharp-edge orifice. With a PFE system, the EGR valve only serves as a pressure regulator, rather than as a flow metering device. The Differential Pressure Feedback EGR (DPFE) system operates in the same manner, except that it also monitors the pressure drop across the metering orifice. This allows for a more accurate assessment of EGR flow requirements.
Fig. 3: PFE/DPFE sensor wiring schematic
Unplug the PFE/DPFE sensor electrical connection.
Turn the ignition key to the ON position, but do not start the engine.
Using a high impedance Digital Volt Ohmmeter (DVOM) set to read voltage, probe the DPFE/PFE terminal of the sensor. The voltage should be approximately 0.45 volts.
Using a hand held vacuum pump, apply 8-9 in. Hg (27-30 kPa).
The voltage should be above 4 volts.
Quickly release the vacuum from the sensor and the voltage should drop to less than one volt in three seconds.
If the readings are not as specified, the sensor may be defective and should be replaced.
Loosen the Exhaust Gas Recirculation (EGR) valve-to-exhaust manifold tube nut at the valve.
Unplug the EGR valve hose.
Unfasten the EGR valve bolts.
Remove the EGR valve and gasket.
Clean the old gasket material from the EGR valve mounting surface.
Install a new gasket and the EGR valve.
Tighten the valve retaining bolts and connect the hose.
Tighten the EGR valve-to-exhaust manifold tube nut at the valve.
Unplug the EVR solenoid's electrical connection.
Tag and disconnect the hose(s) from the EVR solenoid.
If equipped, loosen the retainers and remove the EVR solenoid.
Installation is the reverse of removal.
Pressure Feedback Electronic (PFE)/Differential Pressure Feedback Electronic (DPFE) Sensor
Tag and disengage the hose(s) from the sensor.
Unfasten the retainers and remove the sensor.
Did you do the testing before replacing the IAC?
Did you remove the egr valve and look inside for carbon deposits?
Here is the vacuum routing for the engine, pay particular attention to the hoses and components in the lower portion of the diagram. It is common to have a leak in or around the carbon canister. You might try disconnecting the vacuum source at the throttle body and plug the port on the throttle body and test to see if it helps, that will tell you if you have a leak in those components. Let me know if you find anything.