RE: 2005 Limited, Manual, 51k Miles

I recently purchased this as my long time retirement toy. Completed the 74mm Throttle Body Upgrade. Completed memory reset. Idles as it should until it reaches normal operating temp. Then the idle bounces between 1200-1800rpm for about a minute then it settles down to around 750rpm. Does this every time I come to a stop. Suggestions to remedy? My previous toys were 350z's. I appreciate your knowledge and guidance.