Why does your car feel fine at high RPM but weak down low? Worn spark plugs can cause delayed combustion, vibration at idle, poor cold starts, and engine warning lights. Spark Plug Damage Abnormal Dashboard and Engine Vibration Oil on the Spark Plugs Causes and Fixes Tell tale signs your Spark Plugs are failing Wilco Motosave Bad Spark Plugs Symptoms and Easy Diagnosis Practical Mechanic Your Spark Plug Speaks. Do You Listen? A simple spark plug inspection can reveal a lot about your engine's health. The color and condition of your spark plugs help diagnose fuel