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2005 330xi Auto, 2006 330ci Vert Auto
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As noted in an earlier response, from the factory there are 4 O2 sensors. 2 of them are before the catalytic converter and 2 after. Since your son's car has headers, then he had to have done something with the 4 O2 sensors. You showed 2 dangling O2 sensors. I cannot tell if they are pre-cat O2 sensors or post-cat O2 sensors. Is there anyway you can find all 4 O2 sensors somewhere?

Unresolved questions - you said the car ran great for months, so what changed? Do you know what the "tune" was supposed to do? I can guess that the "tune" eliminated the post-cat O2 sensors due to the headers. So what happened to the pre-cat O2 sensors? I do not think the BMW computer (DME) would operate very well without any O2 sensors.
 
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