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Q: Oil fouls one spark plug - possible cause and recommendations to repair.

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Must replace spark plug (only #4 cylinder) every 600-700 miles engine starts to idle rough due to dirty plug (carbon build up) believe to be from oil leak from damaged valve seal - any recommendatio how to go about repair

My car has 105000 miles.
My car has an automatic transmission.

Hi there. If oil is causing the spark plug on cylinder number 4 to foul out every 600 to 700 miles, then the valve guide seals to that cylinder are damaged and need replaced. The valve guide seals prevent excessive oil from entering the combustion chamber. Most of the time the intake valve guide seal is worn for the oil gets sucked down into the cylinder rather than pushed out. This causes the oil to mist into the cylinder coating the spark plug making it foul out. If you need further assistance with your spark plug fouling out due to excessive oil in the cylinder, then seek out a professional, such as one from Your Mechanic, to help you.

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