BMW Repair: 1999 BMW 540i, fuel filler cap, control thermostat

Question
I notice another Check Engine Light questions and was hoping you could help me with mine.  The car has 81K miles on it and my codes have been coming and going for the last 10k miles and now the Check engine light is on solid.  When the light first start to appear I had it checked and was told the code was "Fuel Distribution Malfunction, Left Bank" and had no idea what was wrong.  So I got my own code reader and now that the light is on all the time the codes are: A4-Ambient Pressure Sensor; 1A-Mixture Control, off Idle, Cyl#1-4; 8C-MAP Control Thermostat Circuit/Control; 16-PreCat Oxygen Sensor Aging, Cyl#5-8; OD-PreCat Oxygen Sensor, Cyl#1-4. So I replaced all four O2 sensor thinking that if I had two bad ones, I should just replace them all and the only code that went away was OD.  Then replaced the Fuel Filler Cap and nothing changed.  Can you help?

Answer
Ray, you have several issues. Replace the thermostat. Your mixture control is most likely an intake system leak. I would remove check the intake manifold for leaks with a smoke machine. If you have heavy oily dirt build up around the gaskets then I would reseal the throttle, front intake gasket, rear manifold gasket and replace rear plate, and finally the four gaskets that mount the manifold to the heads. This is a complete intake reseal. I would also have DME (engine computer) reprogrammed with the latest software. When the intake manifold is off look at the Valley pan and make sure it isn't leaking coolant. Clean the throttle aswell. After this I would expect you to in the clear.
-Evan