I have already posted this in the M5 forum, but I thought I would try my luck here. My passenger side MAFS is not reading the air flow and it is causing my car to run rich. I put brand new BOSCH sensors on last week but it didn't help. When I unplug the drivers side sensor the car stumbles and almost stalls. When I unplug the pass. side sensor nothing happens. I sprayed down the electrical contacts with my CRC MAFS cleaner in hopes of cleaning out some debris, but that didn't help either. Some how the passenger side is not relaying the air flow to the ECU. Anyone had a similar problem? My car is a 2000 M5 with 73k. In search if the rich running condition I have replaced air filters, MAFS, spark plugs and O2 sensors.:help

Have you looked for an intake leak on that side? If enough air is leaking in after the MAF, unplugging it at idle will have little or no affect.

Another possibility would be an aged pre-cat O2 sensor on that bank that has caused a large positive fuel trim. At 73k the car is getting into the range where an O2 sensor is a possibility.

O2 sensors are brand new as of Saturday. That is a great idea looking for an air leak. I will try that out today. Should I use starter fluid or something of the sort to hunt with. Kinda like looking for a vacuum leak?