Causes of Knocking Sound in Engine While Idling

The causes of why an engine makes a knock noise when it is idling. Mechanical Knock or Detonation Knock Mechanical Knock: A mechanical component is broken. Rod Knock (Lower half of engine speeds up with engine RPM. Rod knocks are usually a "thud" dull sound.) Valves (Top of engine more clacking sound than knocking.) Lifter Tap Knocks (Top of engine Lifters are usually high pitched and a "clean" tap sound. Possible Causes Dirty or Low Oil Bad oil pump Wear and tear Detonation Knock: Something causing the cylinder to fire early. Engine Timing Off Bad or slipped timing belt or chain Bad Cam or Crank Position sensor Bad Knock Sensor Carbon Deposits Engine often continues to run when shut off. www.backyardmechanic.org By using this information user assumes all risk of use.