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Commodore (VN-VZ) / HSV

1988-2006 / Sedan / Estate / Australia

All Commodore (VN-VZ) / HSV problems All workshop problems
Common Idle and Running Issues

Rough Idle and Stalling (V6, All Generations)

Symptoms

Engine idles roughly, may stall at traffic lights. RPM fluctuates between 500-1000 rpm at idle. Stalling is worse when the air conditioner is on or at the first stop after a cold start.

Cause

The most common causes, roughly in order of frequency: dirty throttle body (carbon buildup restricts airflow), faulty idle air control (IAC) valve, vacuum leaks from cracked or disconnected hoses, and failing MAP sensor. On the Ecotec, a dirty throttle body alone causes 90% of idle complaints.

Fix

Start with the throttle body.

Remove the air intake duct, spray the throttle blade and bore with throttle body cleaner, and wipe clean.

Do not use carburettor cleaner, it damages the throttle body coating.

If idle remains rough: test the IAC valve (remove and apply 12V to check for plunger movement), inspect all vacuum hoses for cracks, and check the MAP sensor with a scan tool.

Throttle body clean: free.

IAC valve: $50-100.

MAP sensor: $30-60.

Cost mentioned in fix
$50-100$30-60

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Other known issues

Common Idle and Running Issues

Injector Failure (Ecotec V6)

Misfire on one or more cylinders. Rough idle. Check engine light with misfire codes. Fuel smell from the exhaust. Engine stumbles under acceleration.
Common Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Intake Manifold Gasket Leak

Coolant leak at the junction of the intake manifold and cylinder heads. May present as coolant loss without a visible external leak (coolant enters the intake ports), or as a coolant stain on the side of the engine. Engine may run rough or misfire if coolant enters the combustion chamber.
Critical Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Harmonic Balancer Failure (Ecotec, VS onwards)

A wobbling pulley on the front of the crankshaft. Knocking or rattling noise from the front of the engine. The drive belt may track poorly or come off.
Common Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Supercharger Bypass Valve Failure (L67 supercharged V6)

Loss of boost, rattling from the supercharger, reduced performance. The supercharger may make a whining noise that changes with the valve's operation.
Critical Engine, V6 (Alloytec 3.6L, VZ)

Timing Chain and Guide Failure

Rattling noise on cold start that may persist after warm-up. Check engine light with codes related to camshaft timing. Rough idle, misfiring, loss of power. In severe cases, the engine won't start or runs extremely poorly.
Critical Engine, V6 (Alloytec 3.6L, VZ)

Oil Leaks from Timing Cover

Oil weeping or dripping from the front of the engine, behind the harmonic balancer area.
All Commodore (VN-VZ) / HSV problems