540i, M60 engine. Here's what Sometimes the car will start and run normally. Most of the time it will either not start at all or start then stop after a few seconds. Lately the CEL has been coming on and giving codes for O2 sensors, Lambda controls, and Mass Air Sensor. The MAS code appears only after the car is warm and is coasting downhill between 45 and 50 MPH. I can hit the gas a little and the light goes off. The other codes come on at any given time. I have replaced the MAS and both O2 sensors, so I'm suspecting I may have a vacuum leak somewhere after the MAS, a faulty O2 relay, or maybe a bad fuel pump relay. This thing is really sensitive to changes in fuel pressure and unmeasured air getting into the intake. I haven't had a chance yet to do any checks on the relays or possible air leaks. I have checked the wiring from the MAS to the ECM and it's fine. I was getting O2 fault codes the last week of December, so I changed the sensors and the car immediately ran better up until last week, so..... any ideas? Thanks.

exhaust is clauged bad catalitic converter is coroding o2 sensors and causing all the problems

hooly c most mechanics know this where did you go to school

My idea would be to take it to someone who specializes in bmw diagnostics and pay to have it diagnosed.