[s-cars] stumble and smoke at idle

[james McCarthy]

Ok,
New problem. 2 days ago my s6 (full OEM RS2 bits) developed a stumble on initial start up - but cleared within the first 10 seconds or so of driving.  This was associated with thick exhaust. Considered ignition (coil/pos/plugs) or leaking injector.  So replaced the plugs (new bosch F5DPOR) and the stumble seemed to be gone... 
However this am the stumble was back on initial start up only - not as severe and lasted just 2-3 seconds... but now I have "heavy" exhaust at idle even after driving for 10-15 minutes.  No puffs with hard acceleration just at idle... car seems to be running perfectly otherwise pulls strong to redline with full boost and no stumbles...
So where to start - I doubt coil/pos (5 new oem 20K ago)  as I would expect the stumble to persist.  So I'm thinking PCV system as I can't figure why a leaking injector would result in continued thick idle. Also while turbo seals or valve seals are possible - I can't figure how they would cause the initial rough idle.
So plan is to clean out the PVC system (also installing a catch can) and also see if I can determine if an injector is leaking.  Any thoughts or advice would be appreciated.
tia
-jamie