Read up on how pre-cat O2 sensors work and you will understand.what do you mean by perky at cold start? and what do you mean by when they start switching? sorry confused
Use a mechanic’s mirror and bright light.any idea what could be leaking behind the intake manifold?
Correct. The cutover from MS43 to MS45.1 (non-XI models) was 03/2003 production date.All M56 Sulev have MS45.1. I believe only early E46 M54 have MS43, and i believe all XI models run MS43