Power loss on bmw 320d e46

[Dyla NC]

Hi i have a BMW 320d e46 and it has power loss. When i start it in the morning it drives fine but when the heat gauge reach normal temp the cars rpm start dropping when i accelerate.. in evry gear between 1500 and 2000rpm the car struggle and makes a lot of smoke. It also have a rough idle. Can someone please help???