Could check the spark plugs, If they're in a puddle of oil it's your rocker cover gasket. It can also leak the other way onto the hot exhaust manifold, However you can probably smell this when the car is on temperature and it's idling.
Here is the guide if needed:
http://www.projectpuma.com/viewtopic.php?t=9307" onclick="window.open(this.href);return false;
If this is you're problem and you plan on doing it, remember to use a genuine Ford gasket. Aftermarket gaskets tend to fail within months.