That is actually a common problem on the zetec motors. If you have oil in your spark plug galley you likely have a bad valve cover gasket. Now, if you have oil AND gas in the spark plug galley there are all types of problems there because there really is no way for gas to get in there except up through the spark plug hole. That is very likely not why you car isn't idling very well however, check your plugs to make sure they are gapped correctly and not fouled. Check the resistance of the wires and replace if necessary. Hopefully this helps, let me know if you still have problems, I have a zx2 that has the same engine in it.