The IAC is a great place to start. If this doesn't solve your problem check for vaccuum leaks at the fuel injectors and intake manifold. When the engine heats up the seals expand sealing the vaccuum leaks. Other Bricksters have checked this using propane sprayed around the seals on a cold engine. If the engine smooths out when the propane is sprayed around a seal then you have found your leak. A lot of people overlook the fuel injector seals as the primary cause.

The turbos tend to pump oil fumes into the intake system. Over time this will build up in the idle air control (IAC) valve. When it's cold the oil deposites are harder and gum up the IAC operation. Take the valve out and spray the heck out of it w/ brake cleaner until the valve mechanism frees up and starts flopping around. If your rubber turbo hoses air oily it means the turbo bypass valve is bad and this will further agrevate the problem and push oil fumes into the IAC gumming up the internal works and brush contacts.