Idle Air Control (IAC) System Diagnosis. Pontiac Bonneville 2000

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2000 🢒 Bonneville 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Idle Air Control (IAC) System Diagnosis

Engine Controls Components
MAF, IAC, and Knock Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

The powertrain control module (PCM) controls the engine idle speed by adjusting the position of the motor pintle of the idle air control (IAC) . The IAC is a bi-directional motor driven by 2 coils. The PCM pulses current to the IAC coils in steps in order to extend the IAC pintle into a passage in the throttle body in order to decrease air flow. The PCM reverses the current pulses in order to retract the pintle and increase the air flow. This method allows highly accurate control of the idle speed and quick response to changes in the engine load.

Diagnostic Aids

Check for the following conditions:

•	A faulty connection at the PCM or at the IAC valve. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal-to-wire connections. Use a corresponding mating terminal to test for proper terminal tension.

•	Inspect the wiring harness for damage.

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

•

Check the throttle body for objects blocking the IAC passage or the 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 prevent the IAC pintle from fully extending.

•

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

•	Check for a missing oil filler cap or a missing oil level indicator.

Reviewing the Failure 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

The numbers below refer to the step numbers on the diagnostic table.

This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.

Idle Air Control System Check

Step

Action

Values

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Start the engine.
Turn all of the vehicle accessories OFF.
Command the engine RPM up to 1500 using a scan tool, then down to 650, and then up to 1500 while monitoring the Engine Speed on the scan tool.

Does the engine speed remain within the specified value of the desired idle for each RPM command?

± 50 RPM

System OK

Go to Step 3

Disconnect the IAC.
Install a J 37027-A IAC system monitor.
Command the engine RPM up to 1500, down to 650, and then up to 1500 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, a short to voltage, or a short to ground:

•	The IAC A Low circuit

•	The IAC A High circuit

•	The IAC B Low circuit

•	The IAC B High circuit

If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

Go to Step 12

Go to Step 10

Was a low idle symptom or a rich condition noticed?

Go to Step 6

Go to Step 7

Visually and physically inspect for the following conditions:

•	Any throttle body tampering

•	A restricted air intake system

•	A collapsed air intake duct

•	A restricted air filter element

•	Any foreign objects blocking the air intake system

•	Check the throttle body for objects blocking the IAC passage or the 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.

If a problem is found, repair as necessary.

Was a problem found?

Go to Step 12

Go to Step 8

Visually and physically inspect for the following conditions:

•	Any vacuum leaks. Refer to Emission Hose Routing Diagram .

•	Any throttle body tampering

•	Any binding of the throttle Plate or the throttle shaft.

•	A misadjustment or binding of the accelerator cables and the cruise control cables. Refer to Accelerator Control Cable Replacement .

•	A malfunctioning, missing, or incorrectly installed PCV valve.

•	Refer to Crankcase Ventilation System Inspection .

If a problem is found, repair as necessary.

Was a problem found?

Go to Step 12

Go to Step 8

Check for a faulty connection at the IAC harness connector.
If a problem is found, replace any loose terminals as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Was a problem found?

Go to Step 12

Go to Step 9

Replace the IAC valve. Refer to Idle Air Control Valve Replacement .

Did you complete the repair?

Go to Step 12

Check for a faulty connection at the PCM harness connector.
If a problem is found, replace any loose terminals as necessary. Refer to Repairing Connector Terminals in Wiring Systems .

Was a problem found?

Go to Step 12

Go to Step 11

Important:: The replacement PCM must be reprogrammed. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Did you complete the repair?

Go to Step 12

Clear the DTCs.
Start the engine.
Turn all the accessories OFF.
Use the scan tool in order to command the engine RPM up to 1500, down to 650, and then up to 1500 while monitoring the engine speed on the scan tool.

Does the engine speed remain within the specified range of the desired idle for each RPM command?

± 50 RPM

System OK

Go to Step 3