odd thought, but how old is the gas in the tank? I think you said you've been driving it all week, so its probably fresh.
when I got my 318- PO was running 87 octane, and it was probably 2month old fuel. Engine ran like a donkey...
Because of the 87 octane, the engine was retarding the time to compensate. So maybe the timing is off/old gas/I-have-no-idea-but-this-sounded-good-before-typing-it
Patrick ///99 540iA///BMWCCA#465139
98 328i hellrot (sold)
96 318iC black (sold)