PCV valve might help... Do you have a CEL on?
Generally if you have an idle problem, it has something to do with the IAC valve... Which is located on the intake manifold below the throttle body, its kind of a PITA to get to on the zetec, you have to remove the air intake assembly to even see it from the top of the engine bay... Either way, try cleaning that, replace your PCV... and if you have a CEL on get the code scanned... You might also need a new TPS.
Idle problems also can be caused by vaccume leaks.
