Ford Expedition

Hi,
My 2000 Ford Expedition with the 5.4l motor has been idling really rough when its cold in the mornings. Well it has become colder here in Nebraska and I have started to notice that it is now starting to idle really rough all the time. I cant notice any hesitation because I have only had it for a couple months. I was thinking about ordering a new idle air control valve to fix it but not sure if thats totally the problem. It does not have a check engine light on either but it just idles really rough when I am at a stop light. The rpms drop three or four hundred then go up and it just idles like it has a bigger cam. It has never died but I am afraid it is going to. Any ideas on what to check first? I was going to order that new iac valve off ebay since the expedition has 123,000 miles on it and might need a new one.
Thanks

Was it codes P0171 and P0174 . Cuz that's the code everyone I've ever talked with had before they replaced their hose, or elbow.
The easiest way to check for a Vacuum leak is just to climb up onto your fan shroud, reach under all those hoses to the almost the back of your valve cover on the passenger side, and follow it along all the way to the firewall where it goes into the intake. ( With the engine running, so be careful) and you'll know if you have a vacuum leak. Not only can you hear it, you can feel it. It is quite a strong pull on your finger. It might even be collapsed, or cracked.
Just have a feel before you go replacing too many O2 sensors, or IAC's or MAF's or whatever the mechanic tells you you need. It's such a common problem there is a 7 year thread running on another Ford Truck site I am a member on.

I'm not saying this is for sure your problem, but just check it first before you go spending $$$. And make sure you have a new part before you take the old one off, cuz it will crumble in your fingers when you take it off!!!