How to Fix a Misfire or Vibration at Idle

Step by step troubleshooting automotive repair guide on how to fix an engine vibration or misfire at idle, this information pertains to most internal combustion engine vehicles.

Difficulty Scale: 5 of 10

Step 1 - If a check engine or service engine soon light is illuminated read the trouble codes, it could help point the repair in the right direction ie: fuel injector or ignition coil failure.

Check Engine Light

Step 2 - An engine tune up is necessary for proper operation and should be performed according to manufacturer's recommendations.

Spark Plug

Step 3 - Vacuum leaks are a major source of engine idle vibrations, this is because when an engine is at idle it's depending on the intake system to hold said vacuum more than any other time of operation. (When an engine is under load, the vacuum is reduced.) Lift the hood and observe the vacuum hose system and intake gaskets.

Vacuum Leak

Step 4 -  An engine depends on an equal amounts of compression in each cylinder to run smoothly. If poor compression exists in one or more cylinders it can cause rough idle. To check for this condition perform an engine compression test to compare readings. Once a low cylinder has been detected an internal engine inspection is required.

Compression Test

Step 5 - An intake valve must seal completely or intake gases will contaminate the intake charge of other cylinders causing the engine to idle rough, to test this condition a leak down test must be performed. If positive results are produced for leakage, a valve job must be performed.

Intake Valve Cutaway

Step 6 - An engine mount is used to suspend the engine in rubber to help eliminate vibration naturally produced while running. If this mount fails it will allow the engine to rest against the frame of the vehicle causing a noticeable vibration. Inspect the engine mounts for integrity, look for any oil, cracks or separation of the mount.

Engine Mount

Step 7Inspect Balance Shaft Timing - A balance shaft belt or chain is used inside of some designs to counteract vibrations created by the natural engine operation. Balance shafts are operated by a timing belt/chain that can break or become out of correlation with the crankshaft either by worn timing components or misalignment when assembled. To inspect for this problem, remove the timing belt cover and inspect timing belt marks for proper alignment, all engines are different, consult exact alignment specifications.

Helpful Information

An engine is designed to run balanced to minimize vibration felt by the passengers and other mechanical components. This vibration is the most noticeable when the engine is at idle, some components are designed to help minimize engine vibration.

In remote vibration cases, a harmonic balancer or flywheel/flex plate can become unbalanced.

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