Lopey idle on startup, possible causes?

It only happens within the first few minutes of starting it. Idle will surge from 1500 and drop down to below 600. It actually stalled itself yesterday. Forgive my ignorace, but a lot was done to the car before I bought it, including a cam, and I am not certain which cam it has.After a few minutes, it resumes normal cammed idle of a steady vibration at roughly 800 rpm. My initial guess is that the computer is not calibrated to the new cam, or that I need to do an idle reset. Ideas??
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Yeah man, I had a similar problem with my 93 Gt. I have a TFS Stg 1 cam in mine and had the same problem. The thing is, the car is used to the old cam. Everytime you start up your car, it will do that for ahile. You gotta get someone to adjust your idle or you do it. This will compensate for the computer thinking you still have the stock cam in your car. Now I am not saying it will not go down and then come back up......the car just has to find the idle, that's all. After it sits there for about 1-3 mins, it will adjust on its own. Do not buy a chip, becasue that is what I was going to do until I talked with a Mustang Expert here where I live. Adjust the idle and please have someone that knows Mustang do it. Hope this helps you out.
rough idle that doesn't go away is usually a vaccum leak, check intake manifold, and vaccum hoses for leaks.

Hanging idle is probably the IAC, also clean your maf wires specially if you ever had a K&N style reusable filter which has oil on it.