if you replaced 1 and it fixed it you got lucky and I would bet all are right behind it with being dirty. all of them probably need a cleaning

I have used Mr. Injector in Idaho for my M3 cleaning and they came back beautiful, before/after flow numbers new caps and orings.

That reminds me, probably should send the X5 ones out since I got 230K on it now

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2004 X5(E53) 3.0L
1999 M3(E36)
2003 Z4(E85) 3.0L