Your FIAV is bad. Its the bottom part of the throttle body that contains the IAC and the FIAV. The FIAV is the part that raises your idle on a cold start. Once the coolant that flows thru it warms up, the wax in the FIAV shuts the ports letting extra air in.
When the FIAV goes bad or dirty, it keeps the ports open or partially open, so air gets thru and into the intake manifold. That raises the idle and when it reaches 1200 rpms it hit factory set fuel cut for idle and it bounces to low rpms. Then the whole process repeats.
http://www.kylejharper.com/index.php...:dsm&Itemid=55
http://www.dsmtuners.com/forums/arti...e-problem.html