My z4 2.5i only have a code p0174 I don't know what can coused.
P0174 Fuel trim too lean Bank 2
Bank 2 are cylinder 4 cylinder 5 and cylinder 6, Check the sparkplug condition and replace if worn. and use what it is called for.
On this BMW the sparkplug are check for its condition , This one coded a lean Bank condition P0171 , checking the sparkplug for normal wear what was found was 1 sparkplug not properly torque down. which did not set a misfire code at all just a lean bank code
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