Intermitant rough idle, stall....no codes

[Cochrane]

Good Day all,

E39 2003 540iA with 265000 kms. Left outside during a bitter cold snap here in Canada -30C for three days. Upon start up, starter went (changed out) then rough idle with O2 sensor right bank upstream went - took several days for code to appear (changed that). Now running a bit better, but has an intermittent rough idle that will eventiually (3minutes) stall out.....worse part no codes. Runs excellent under load with no noticeable power loss or excess gas consumption. MAF? Camshaft sensor? Vacuum leak? VANOS? Anyones help into the matter is greatly appreciated.