Causes: If the engine starts, but does not run smoothly, it means that the spark plug and ignition system are in order and you need to look elsewhere for the source of the problem. The usual culprit is air intake or fuel system related.
Bad or Dirty Spark Plugs: Spark plugs are responsible for igniting the fuel in the combustion chamber. If they are not working correctly or are dirty they don’t ignite the fuel cleanly and the car can misfire or sputter. … Vacuum Leak: A leak in the vacuum system can lead to a sputtering or rough running engine.