My car shakes and I was told that it's probably from my engine misfiring in one or more of the cylinders.It was recommendedthat Ifirst change the plugs, wires, and distributor cap. I haven't done that yet, so I don't know if that will fix it. But, I was also told that if changing thosedoesn't fix it, I probably have a burnt valve. How do I get that fixed (I'm just wondering incase that's what it is so I'm prepared)? Does it have to be done at a shop?