I would suggest cleaning the IAC valve first. I don't know where it is on the zetec but it will be right around the throttle body. Hopefully it's easy to get to.
edit: couldn't find a how-to with working pictures but that certainly looks like a pain to get to. Not the worst though I'm sure. You don't have to remove the manifold, but You'll be getting at it from the bottom. It's on the plastic manifold on the back of the engine. Here's a good picture I found of it at least.