Q: 99 mercury sable 3.0 ohv is skipping. Change my spark plugs and wires plus the ing Coil. It is still misfiring in cylinder

You should check for fuel injector pulse at the injector with noid light connected to the injector connector. Retest system after clearing the codes to make sure the codes return for misfires on cylinders 3 and 4. The spark plug cables should be verified they are connected to the coil correctly or the #3 and #4 wires are crossed on the coil. If they were on wrong then clear codes and retest the system for clear codes and no misfires.

Hi there. If the coil, plugs, and wires have been changed then it sounds like there may be a mechanical concern. Do the same codes return? Same cylinders? Does the exhaust have a strong fuel smell? Broken/severely leaking injectors could be dumping fuel into the cylinder. Check the oil and smell for fuel as some of the fuel will enter the crankcase. If this is not a fuel injector concern, then it will need appropriate mechanical testing to determine if the compression is within spec, if there is cylinder leakage, and determine the best course of action. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a misfire inspection.