My M3W is also a 2014, and suddenly began the hard starting scenario. Not long after, the front pulley bolt unscrewed itself through the front cover requiring the front pulley upgrade kit with new pulley and belt...What I found when installing the new pulley, is that the drive design between the crankshaft and pulley is marginal, in that it is just 2 flat spots on the crank which drive matching flat spots in the pulley bore. This had got worn or hammered, and resulted in an estimated 3 or 4 degrees of play in the pulley (no wonder the bolt unscrewed itself). What I did on assembly was put JB Weld epoxy in the pulley bore at assembly to fill the gap in the flat spots. I am still not sure how well it will hold up under the temperatures, but so far so good. After this replacement, no more hard starting.
The next place you might check is the front pulley. Try to determine if there is rotational slop. And make sure it has the bolt upgrade kit installed.
