Does yours have a secondary air injection pump? Emission changes are probably why the intake ports on mine are all plugged. With so much plastic, a smoke test may be worth it. Even a plastic solenoid can work and leak internally. I'll dig through removed parts. I say old O-rings can be a problem. A few connections came off way too easy. Some connections didn't

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'06 X5 3.0i - bought @143,123 miles (12/26/20)