Posted on 1/30/2026
When an engine starts running rough, most drivers jump straight to the spark plugs. That makes sense because plugs are common wear items. But ignition coils fail plenty often, too, and the symptoms can overlap in a way that makes guessing expensive. The good news is your car usually gives a few clues that point more toward plugs, more toward coils, or sometimes a different problem entirely. How Spark Plugs And Coils Work Together Spark plugs create the spark that ignites the air-fuel mix in the cylinder. Ignition coils provide the high voltage that makes that spark happen. In many modern cars, each cylinder has its own coil sitting on top of its spark plug. When everything is healthy, the spark is strong and consistent. When either part starts failing, combustion gets inconsistent, and that’s when you feel the roughness. Because the coil and plug work as a pair, a weak plug can stress a coil, and a weak coil can foul a plug. That’s why it’s smart ... read more