Hi there, I have a 2012 Cadillac CTS Coupe 3.6L which has 70k miles on it.  Auto trans. and runs great however, when cold @ idle it runs really rough until the computer seems to regulate the rpm to keep it from dying.  NO CODES!  When the car is driven and warmed up the problem seems to kind of get better but not fully resolved.

I have gone through these steps...  Cleaned throttle body and MAF sensor.  Changed spark plugs with AC Delco plugs and gapped them correctly.  Changed the vapor canister purge valve.  Checked all vacuum lines to verify no vacuum leaks.  Serviced the Transmission and also had the torque converter look at.  Motor Mounts pass visual inspection without any movement.  The computer doesn't show any codes.  Ran a complete diagnostic with Professional scan tool and everything came up normal without any codes or concerns with live data.

I always use premium gas and haven't tried cleaning fuel injectors or changing coils yet.

It's a mystery to me and if you could give me any insight I would really appreciate it.

Thanks, 

Brandon