Long Term fuel trims at -8% ??

That's not right...that tells me it is running RICH.. The minus sign says that based on O2 readings the DME is removing fuel from the air/fuel ratio.

Ideally, the Long term trim should be about +2-3% after warm-up.

I would check fuel pressure at the rail...should be close to 50psi...We had a bad batch of Hengst fuel filter/regulators that resulted in 60 psi and a rich condition.

If your fuel pressure is good..Get your injectors tested or replaced.

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'03 530i - manual swapped - 425k miles
'06 325Cic auto 115k
'05 X5 3.0 auto 158k
'99 E39 528i 5-speed 130k