Engine Vibration Caused By Spark Plug Car Shaking After Changing Spark Plugs: 5 Possible Causes Why Is My Car Shaking at Idle? What are Common Symptoms of a Bad Spark Plug? 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. Common Symptoms of Bad Spark Plugs & Why You Shouldn't Ignore Them! Bad spark plugs can seriously affect your car's performance and even lead to engine damage. Here are the