Mechanics

Idle Vibration or Misfire

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Step by step troubleshooting automotive repair guide on how 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

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-07-10)