I had a hesitation/stumble on my 98 Contour (2.0L Zetec) for the past year. After trying changing the plugs twice ( Autolite and Bosch double plats), with no relief, I finaly took the advice of some here and put in a set of original factory plugs. VIOLA!!! My car now purrs!!
Examining the plugs, they are very much differnt than the aftermarket plugs. The center electrode is very thin.