If you give it more gas when you are doing these manouvres it will stop,when the engine is idling you are expecting it to still drive the p ower steering pump,the cars weight,the water pump,alternator etc etc.All smaller engined cars can have this trouble with engine loading,you have to adjust your driving style.It sounds as though this car has a system that automatically copes with the engine idling ,this may have failed,but giving it more gas at these times will over.ride the problem until you can get it sorted.