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I have a similar slight miss at idle, especially when car sits for a a week or so. Mine doesn't knock or ping whatsoever but I had dealer look at mine. The did not find anything wrong at all and once you drive the car regularly it pretty much goes away. Their analysis tool says they have a smoothness parameter and two cylinders were slightly below the other four cylinders on the smoothness gauge but well within the spec. So all they told me that that I have the original coils which have been upgraded now and that I also have the original injectors which in the US have had the warranty extended and replaced with index 12. First, I assume by knock you mean pinging/detonation, not an actual knock like a rod knocks? If the car is truly pinging/detonation and the ECU is not doing anything about it, then it's probably ok to replace the knock sensor, but the knock sensor wouldn't cause the miss at idle. It just retards the timing if it detects detonation.
If you have the original coils, I would replace the coils and plugs first with the latest Delphi coils for 1M. The first version they revised them with were made by Eldor but apparently they didn't work as well as expected so currently, the BMW O.E. Delphi made coils are your best bet and use BMW OE spark plugs which are made by Bosch.
It can't hurt to update the plugs and coild but I would consider injectors first and foremost. These are weakpoint in the 1M. If you have an injector that is underperforming, it could cause detonation. Direct injection is amazing because it allows you to run high compresession and boost that you couldn't do before. By putting the injector in the combustion chamber, the ECU can immediately adjust fuel charge to cool the cylinder and prevent detonation but if an injector is not working correctly, that cylinder will run hotter and could detonate.
Bad coils and plugs can cause misfires and bad performance but not likely to cause detonation unless they are so carboned up that they become a glow plug.
So if you just had a miss at idle I would change coils and plugs, especially if you have the outdated coils but if you actually have pinging/detonation, I would look at injectors next as the cause of the detonation.
A lot of people will bring up carbon build up which could cause the rough idle but I don't think that will cause detonation. In old cars, carbon build up would happen in the cylinder which raises the compression of the cylinder but with direct injection, the carbon buildup happens in the intake manifold so you would get less air into the cylinder which would make more a richer fuel mixture which prevents detonation. On the other hand, if you have a substandard fuel injector that is not spraying enough fuel, that could the cylinder to lean out and detonate.
The injectors could also cause a miss at idle.
So my educated guess would be to look at injectors, then plugs and coils.
Best wishes and let us know what you find out so we can all share information.
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