So just to keep you'll up to date, am now on my second tank with Esso 89 instead of the usual #91 and thus far no more misfire codes, stumbles somwhatnstill on cold mornings but looks like my engine likes the lower octane better, will take the next step down to 87 on my next fill up.

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E39 528i 1998, 5 spd black, 350Kkms and going..with new owner.
E60 545i 2004, 6 spd steptr. mystic blue, Tom Sellick's old car, Adaptive steering, Adaptive Xenons, Anti dazzle mirrors and FAST!!!, BT&Aux+SB Chime+Dig speedo+iDrive discl. Coded