2001 BMW 325xi - Car won't start right away

I have ben having an issue where the car turns over but won’t start on the first three or four tries but then starts. A diagonistc was run but did not show any problems. I have had the fuel pump and fuel regulator replaced, but this did not solve the problem. It seems to happen more since the weather has turned cold. Generally if the car has been started once in the morning it is fine the rest of the day, but a twice the car has stalled a few times in the afternoon before starting. Does anyone have any idea what it could be?