Try some octane booster. When I was in Mississippi over a year go the stations there sold a 94 octane gas and Boy Howdy did my X like it. Peppy and ran much smoother. Perhaps your engine just can't stomach 91 with ethanol. Or maybe try 100% gas and see if that makes any improvement.

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2001 3.0i * SOLD *
Current
2010 E83 Alpine White