Idle vibration occurs when one or more systems fail to maintain stable RPM.
1. Worn Engine Mounts (Most Common Global Cause)
Mounts isolate engine vibrations.
Facts
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Rubber mounts degrade from heat
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Hydraulic mounts leak fluid
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Failure increases vibration 2–4x
2. Misfires at Idle
Misfires cause uneven combustion.
Causes
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Failing spark plugs
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Ignition coil problems
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Vacuum leaks
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Fuel injector imbalance
Evidence
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Rough idle
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Shaking steering wheel
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Check engine light
3. Dirty Throttle Body
Carbon buildup disrupts airflow.
Symptoms
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RPM fluctuations
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Idle drop when AC is turned on
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Delayed throttle response
4. Vacuum Leaks
Unmetered air causes rough idle.
Common Leak Points
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PCV hoses
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Intake manifold gasket
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Vacuum lines
5. Low Compression in One Cylinder
Uneven compression causes shaking.
Measured By:
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Compression test
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Leak-down test
Conclusion
Idle shaking is usually due to engine mount wear or misfires, followed by vacuum leaks or throttle issues.
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