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      11-29-2012, 02:13 AM   #10
TwinT1addict
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Drives: 2008 135i
Join Date: Apr 2008
Location: Stamford, CT

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2008 135i  [3.50]
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Could be your hpfp or you can have bad carbon build up on the valves. Carbon deposits on the valves will cause pre-detonation of the air fuel mixture and lowers fuel economy. Like the other guys mentioned start with the plugs first them work your way up. To me it sounds like the hpfp on its way out if it was no changed earlier. Best of luck to you.
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