Why Is My Car Shaking at Idle? Reading a spark plug is a great way to check your engine's health. Mechanics often read spark plugs to diagnose fuel mixture, ignition, and engine condition. Here's a clear guide for Tell tale signs your Spark Plugs are failing Wilco Motosave Why Is My Car Shaking and How Do I Fix It? Metropolitan Garage Spark plugs the 'small giant' of the powertrain Professional Motor Mechanic