I am a new diy mechanic... The check engine light is on. Sometimes it flashes and sometimes it goes away. The diagnostic says that it is a cylinder misfire and the cylinder that is misfiring changes with each diagnostic but at some point each one has misfired. I have replaced the spark plugs twice and the wires twice and the light (and hearing/feeling it misfiring) stops for a few months but then starts up again. Any ideas what this could be? Have you experienced this before?