Idle Air Control (IAC) System Diagnosis. Oldsmobile Intrigue 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.5L 🢒 Idle Air Control (IAC) System Diagnosis

(IAC) Valve, Engine Oil Level Indicator Switch, Engine Oil Pressure Switch
Engine Controls Components
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The PCM controls engine idle speed by adjusting the position of the Idle Air Control (IAC) motor pintle. The IAC is a bi-directional motor driven by two coils. The PCM pulses current to the IAC coils in steps (counts) to extend the IAC 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.

Diagnostic Aids

Use the Connector Test Adapter Kit J 35616 for any test that requires probing the PCM harness connectors, electrical center fuse/relay cavities, component terminals or a component harness connector. Using this kit will prevent damage caused by improper probing of connector terminals.

If the problem is intermittent, refer to Intermittent Conditions for diagnosis.

Check for the following conditions:

•	Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

•	Damaged harness. Inspect the wiring harness for damage.

•	Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.

•	Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate.

Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.

•	Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed PCV valve, leaks at intake manifold brake booster hose disconnected, etc.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Idle Air Control System Check

Step

Action

Value(s)

Yes

Did you perform the On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

Start the engine.
Turn all accessories Off (A/C, Rear defroster etc.).
Using a scan tool, command RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does Engine Speed remain within the specified value of Desired Idle for each RPM command?

± 100 rpm

System OK

Go to Step 3

Leave the engine running.
Disconnect the IAC.
Install the J 37027-A IAC System Monitor node light.
With the engine running, momentarily blip the throttle while observing the IAC System Monitor node lights.

Does each node light cycle red and green (never OFF)?

Go to Step 5

Go to Step 4

Check the following circuits for an open, short to voltage, or short to ground:

•	IAC A Low.

•	IAC A High.

•	IAC B Low.

•	IAC B High.

If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found and corrected?

Go to Step 12

Go to Step 10

Was a low idle symptom or rich condition noticed?

Go to Step 6

Go to Step 7

Visually/physically inspect for the following conditions:

Throttle body tampering.
Restricted air intake system.
Collapsed air intake duct.
Restricted air filter element.
Foreign objects blocking the air intake system.
Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate.

Was a problem found and corrected?

Go to Step 11

Go to Step 8

Visually/physically inspect for the following conditions:

Vacuum leaks.
Throttle body tampering.
Throttle Plate or throttle shaft for binding.
Accelerator and Cruise Control cables for being misadjusted or for binding.
Faulty, missing, or incorrectly installed PCV valve. Refer to Crankcase Ventilation System Diagnosis .

Was a problem found and corrected?

Go to Step 11

Go to Step 8

Check for a poor connection at the IAC harness connector.
If a problem is found, replace faulty terminals as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found and corrected?

Go to Step 12

Go to Step 9

Replace the IAC valve.

Is action complete?

Go to Step 12

Check for a poor connection at the PCM harness connector.
If a problem is found, replace faulty terminals as necessary. Refer to Intermittents and Poor Connections Diagnosis . .

Was a problem found and corrected?

Go to Step 12

Go to Step 11

Replace the PCM.

Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

Go to Step 12

Start the engine.
Turn all accessories Off (A/C, Rear defroster etc.).
Using a scan tool, command RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does Engine Speed remain within the specified value of Desired Idle for each RPM command?

± 50 rpm

System OK

Go to Step 3