The IAC sensor or IAC valve plays a fundamental role in the regulation of engine idling speeds, by administering and regulating the entry of air into the combustion chambers. When the IAC sensor fails, several engine problems occur. If the IAC sensor fails due to dirt, it will be very simple to solve the problem, simply disassemble the IAC sensor and clean it with a clean flannel. The electrical failures of the IAC valve may be due to one or both windings of the stepper motor being short-circuited or opened, leaving the IAC valve in a single position, which can cause the motor to be at low revs or accelerated, In this case there is nothing left but to replace the IAC valve completely. To verify if the IAC sensor has this last fault, you can use a multimeter and verify that the windings are with the appropriate resistance values, whose value is about 75 ohms in each one, if it has a value less than 10 ohms then the IAC sensor encounters a short circuit fault, while if the multimeter marks high resistance it will be because the IAC sensor is with the burned or open coil.
What is year--make--model? Any applicable trouble codes? So your having trouble with idle? Remove throttle body, clean throttle bore and any small passages. Check and clean anything that has to do with idle air system.
DTC P1519: IAC Valve Circuit Malfunction
Turn the ignition switch ON (II).
Is DTC P1519 indicated?
YES -
Go to step 3.
NO -
Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the IAC valve and the PCM.n
Turn the ignition switch OFF.
Disconnect the IAC valve 3P connector.
Turn the ignition switch ON (II).
Measure voltage between IAC valve 3P connector terminal No. 2 and body ground.
Is there battery voltage?
YES -
Go to step 7.
NO -
Repair open in the wire between the IAC valve and the PGM-FI main relay.n
Turn the ignition switch OFF.
Check for continuity between body ground and IAC valve 3P connector terminal No. 1.
Is there continuity?
YES -
Go to step 9.
NO -
Repair open in the wire between the IAC valve and G101.n
Disconnect PCM connector B (25P).
Check for continuity between body ground and PCM connector terminal B23.
Is there continuity?
YES -
Repair short in the wire between the IAC valve and the PCM (B23).n
NO -
Go to step 11.
Connect IAC valve 3P connector terminal No. 3 to body ground with a jumper wire.
Check for continuity between PCM connector terminal B23 and body ground.
Is there continuity?
YES -
Go to step 13.
NO -
Repair open in the wire between the IAC valve and the PCM (B23).n
Remove the jumper wire from the IAC valve 3P connector, then reconnect the IAC valve 3P connector.
Turn the ignition switch ON (II).
Measure voltage between body ground and PCM connector terminal B23.
Is there battery voltage?
YES -
Substitute a known-good PCM and recheck. If the symptom/indication goes away, replace the original PCM.n
NO -
Replace the IAC valve.n
Operation
The Idle Air Control (IAC) valve controls the amount of air that bypasses the throttle valve, which controls the engine idle speed. The IAC valve consists of windings, an armature, a return spring, and a rotary slide. The engine control module (ECM) pulses the voltage to the winding, the opposing forces on the armature by the return spring cause it to maintain a fixed position, adjusting the amount of bypass air to maintain the correct idle speed.
Removal & Installation
Testing
Checking Idle Air Control Valve (IAC) Triggering
Fig. IAC Connector
Fig. Showing the IAC Valve
WARNING
Do NOT check for ease of movement by prying on the rotary slide with a screwdriver or other tools that could cause scratching or other damage.
OPERATION
The Idle Air Control (IAC) is a bi-directional motor driven by two coils. The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.
Fig. Typical Idle Air Control (IAC) valve components
During idle, the proper position of the of the IAC pintle is calculated by the PCM based on the battery voltage, coolant temperature, engine load and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the ignition switch is cycled ON and then OFF . When servicing the IAC, it should be disconnected or connected with the ignition switch OFF in order to keep from having to reset the IAC valve.
The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. A Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with hard starting and a rich air/fuel ratio. Again, a Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.
TESTING
As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items a non-professional should check before taking the vehicle to a qualified technician for diagnosis and repair.
Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection.
Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed.
Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system.
Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate.
Check for vacuum leaks such as disconnected hoses, leaks at the EGR valve and EGR pipe to the intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold brake booster hose connection, etc.
REMOVAL & INSTALLATION
Fig. The Idle Air Control (IAC) valve is mounted on the throttle body-3.8L (VIN K) engine shown, others similar
NOTE
Before installing a new IAC valve, measure the distance that the valve is extended. The measurement should be made from the motor housing to the end of the valve cone (pintle). The distance should be no greater than 1 1 / 8 inch (28mm). If the pintle is extended too far, adjustment is required, otherwise damage may occur when the IAC valve is installed. Adjust the IAC valve by compressing the pintle to achieve the correct length.
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