There is a Hyundai spark plug for each cylinder your engine has. Without this spark plug, the compression of your air/fuel mixture would be meaningless. On today's modern internal combustion engine used by Hyundai, the energy that creates the spark is from the onboard computer. This energy is transferred to the ignition coil through the spark plug wires to the plug's electrode where the arc is formed. Each part of this system must be working at or near top efficiency for the engine to perform as expected. When an engine is running rough, the first and easiest thing to test is the Hyundai spark plug. This is done by pulling the plug, grounding it on the engine, and reconnecting the wire. With the engine running, you should observe a spark being generated at the electrode. If the spark is weak or nonexistent, then another plug should be tested on the same wire. If the new spark plug tests ok, the old plug is faulty but you know the wire is good along with the ignition coil. This needs to be done to each plug on the Hyundai engine. It really is that simple to cure a rough running engine when the faulty part is the plug. This test also includes the testing of the wires used to transport the spark and the ignition coil. In rare occurrence the problem with the spark generation is the onboard computer. While they do fail, most of them last the lifetime of the vehicle. One word of caution to the Hyundai owner, the spark plugs are durable but must be handled with care. If one is dropped it should be replaced. If the ceramic portion of the plug is compromised, it will not be capable of generating a spark.