Just a couple of quick and easy things you can check. If you have a hand controller, try changing the return to idle fuel cut off. Try increasing or decreasing it and see if it has any effect. From memory that should be on the screen where you set the idle. Also make sure that your car is idling at what your set point is. E.g if the controller is set at 800rpm but the engine is idling at 850, adjust the iacv so that the idle matches the set point. This had happened on a previous car of mine and was causing all sorts of weird idle issues. I adjusted the iacv to match and it ran beautifully.