Originally Posted by Dackelone
Your car probably has the early injectors - which were not the greatest. Changing all six isn't a bad idea. They will need to be coded once installed. There was a recall for the dealers to check ALL the injectors and update them IF necessary. You might not get all six replaced.... but sometimes they will. It depends on the serial numbers of the old injectors.
Most people are changing the coils at ~80K miles. With high miles it is not a bad idea either. I would only change them once they start to cause an issue though. Cobb and Bav Auto sell red HP coil packs. I don't know IF they are any better them OE ones though.
I really think this cold start issue is spark plugs. OP - when you change your plugs - did you use BMW bought plugs? Sometimes the OEM (aftermarket) plugs cause issues like this. Just look at my "changing spark plug DIY" to see why.
From what I read online most people say that cold start issues are leaky injectors because the car sits overnight and injectors leak. This issue only happens when the car has been parked for a long time, when car is parked for 2-4 hours no issues in starting.