What should the cold compression test readings be on an 83 380SEL.If compression comes back low, is it usually burned valves or maybe just adjustment. I can hear valves tapping on both sides. Engine runs very rough (like it is only firing on 5 or 6 cylinders) Have you ever heard of valves being so far out of adjustment that this would happen(skip, rough idle, loss of power)? What would cause this? Ignition parts(wires, plugs, cap, rotor) have been replaced. Also if I have to get a valve job, wht is it going to cost?(ballpark figure) I live in Northern Florida.