Idle Air Control (IAC) System Diagnosis. Chevrolet Monte Carlo 2000

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Monte Carlo 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Idle Air Control (IAC) System Diagnosis

Refer to

IAC, Engine Oil Level, Engine Oil Pressure, EGR, EVAP Vent

ABS/PCM, STOP, TURN SIGNAL and SRS Fuses
G113 - Continued
Handling ESD Sensitive Parts Notice
Engine Controls Components
Powertrain Control Module Description
VSS, Cruise
Engine Data Sensors - MAF, EVAP Purge, Air Injection
OBD II Symbol Description Notice
.

Circuit Description

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

Diagnostic Aids

Inspect for the following conditions:

•	A poor connection at PCM or at the IAC motor. Inspect the harness connectors for the following conditions:

•	Backed-out terminals

•	Improper mating

•	Broken locks

•	Improperly formed or damaged terminals

•	Poor terminal-to-wire connections

•	Refer to the Testing for Intermittent Conditions and Poor Connections and Connector Repairs and Wiring Repairs .

•	A damaged harness. Inspect the wiring harness for damage. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs and Wiring Repairs .

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

•	The throttle body. Inspect 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.

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

•	A vacuum leak. Inspect for the following conditions that cause a vacuum leak:

•	Any 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

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 number below refers to the step number on the diagnostic table.

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

Step

Action

Values

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Start the engine.
Turn all the accessories OFF, including the A/C, the rear defroster, etc.
Using a scan tool, command the 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 value of the desired Idle for each RPM command?

50 RPM

System OK

Go to Step 3

Disconnect the idle air control (IAC) valve.
Connect a J 37027-A IAC system motor analyzer to the IAC harness connector.
With the engine running, command the RPM up to 1500, down to 650, and then up to 1500 while observing the J 37027-A IAC system motor analyzer lights.

Does the J 37027-A IAC system motor analyzer light cycle red and green, but never OFF?

Go to Step 5

Go to Step 4

Test 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 .

Did you find and correct the condition?

Go to Step 12

Go to Step 10

Did you notice a low idle symptom or a rich condition?

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

•	The throttle body 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.

If a problem is found, repair as necessary.

Did you find and correct the condition?

Go to Step 11

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

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

•	A faulty, missing, or incorrectly installed PCV valve. Refer to Crankcase Ventilation System Description .

If a problem is found, repair as necessary.

Did you find and correct the condition?

Go to Step 11

Go to Step 8

Test for a poor connection at the IAC harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

Replace the IAC valve. Refer to IAC Valve Replacement .

Did you complete the replacement?

Go to Step 12

Test for a poor connection at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 11

Important: : The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Did you complete the replacement?

Go to Step 12

Clear the DTCs.
Start the engine.
Turn all of the accessories OFF, including the A/C, the rear defroster, etc.
Using a scan tool, 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 engine speed remain within the specified value of the desired idle for each RPM command?

50 RPM

System OK

Go to Step 3