With a thick glove on your hand while the engine is idling, pull off one spark plug boot at a time and see if the engine is affected. The one that has no further affect (weakening the idle) is the problem "child". See if that wire is leaking electric to a ground point somewhere, if so, change out ALL the plug wires. If not, replace the spark plug.
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With a thick glove on your hand while the engine is idling, pull off one spark plug boot at a time and see if the engine is affected. The one that has no further affect (weakening the idle) is the problem "child". See if that wire is leaking electric to a ground point somewhere, if so, change out ALL the plug wires. If not, replace the spark plug.