Finish changing your plugs, and also change the coils. 545's sometimes idle roughly in the cold. I finally cured mine by getting an active autowerkes tune. It really helped. The back plugs are tough, but you need a good flexible socket. You can also pull the plug out with the coil.

 

Tough is a underestimation! The back plugs is a nightmare. Took me over an hour just to take the far back one out. Was about to drop the engine to replace the plugs hehe.
The car is running fine now! Finally had the chance to open up the throttle and race an RS5

 

The 62N series temps are about 105 107 f C or 220 to 230 f. BMW's objective was to reduce NOX emissions by running the engine hotter.

 

NOX is reduced with EGR (external or internally, as in the N62). Higher temperatures produce MORE NOX, not less, as the higher temperatures actually increase the reaction with the Nitrogen in the air. Since the reaction is an "equilibrium" reaction, recirculating part of the exhaust gases limits the production of NOx's.

Respectfully, Bob P.