This happens occasionally to all BMW models. If it was intermittent, the code will clear on its own after x amount of recycles (start/stop engine). Sounds like you had *something* unusual happen. Bad gas causing a slight misfire, slight misfunction in coil pack, etc... You might have to replace something shortly - either a plug or pack. Suggest waiting for it to clear (or have AutoZone clear it) and see if it pops up again before doing anything.

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'03 X5 3.0, '98 M3 vert, '02 Audi TT, '99 323i