carb, thottle

I have my idle set at 1600 rpm on the ground, but when flying a landing approach and throttled all the way back the rpm never goes lower than about 2200. I believe this is because the prop is windmilling and pushing the engine to higher rpms. Totally normal.

My idle speed is 1800 and  my warm up speed is 2000, when i drop back dow to my idle speed , it wand to drop below and cause  the eigne to run rough 

Double check your idle speed jet settings and re do your carby balance.

Note: I feel that, without changing any settings, idle speed changes as ambient temperatures change ie summer temps will have a lower idle speed than winter. Ideally you would have a "stop" adjuster on your throttle, to accommodate this small temperature related change.

When I weigh floats at annual and already have the carb bowl off I always take out the idle jet and clean it. It just unscrews. I find at least 50% + of them have partial to full cloggs. It just takes a couple minutes to do. This issue with blocked idle jets are easier to see on carb sync gauges vs something like a CarbMate. 

The other item that cause carb sync issues is the Mfg's throttle system setup. Some throttles go back to the same position as it opens and closes where some are just too variable which makes a good sync hard to achieve because it never goes back to the exact spot every time. The first time I ran into this in the late 1990's it drove me nuts trying to get a perfect sync.