Try this - hope it helps
Rbooth / Duggmark,
if you have not done so - please try it !! It sounds like the troubles I've been having since 3 yrs ago - when I got the car,same 520i M50 engine.
Just to recap - feels like it's running on 5 cyls, when it's cold it fine when temp is up crappy idling etc. I take it the fuel consumption has been affected.
Now for the Co2 adjustment..only way is to hook up modic II and have that setting in the ECU re-adjusted.IF you have starting problems (difficult) and
moving off in 1st gear -where it seems like hesitation on the border of stalling - then it's most definitely what I had. A CRAPPY Carbon Canister / Charcoal Canister. Remove the hose from the fuel tank that leads IN to the canister, bypass the canister / eleminate it run the hose directly into the purge valve, the other end of tube remains going into the TB.
Try that and see what happens. I did mine a few days ago WORKED Like a CHARM. no more poor starts,takes off from standstill like a grey hound in heat.
I used to have oil in the intake (large amounts) that were also weeping thru the seals (cylinder head) No more..also no more of that engine oil smell in the air after you've driven it hard.
it's great my FC has improved big time. Try it chaps..I hope it works for you.