Cleaner,
I can see that we are going to become good friends. You are a very sharp individual. I apologize if I came on too strong but when I post information I'm always very careful to only make factual statements because I know that a lot of times people on here take what we say as the truth and they do no further research.
All of that being said I understand why there is confusion over the term "MAP" American car manufacturers and even some foreign commonly use MAP sensors. MAP standing for Manifold Absolute Pressure. BMW however does not. BMW uses the MAF (mass air flow) sensor combined with an intake temperature sensor (on this management system it is built into the MAF) along with throttle feedback potentiometers in order to come up with a "calculated" MAP-Manifold absolute pressure. There is no actual MAP sensor and therefore there can not be a Fault for that sensor.
Now the confusion lies here. BMW DOES use a MAP-controlled engine coolant thermostat. It is an electronically controlled coolant thermostat as opposed to the earlier convention style "Wax" cylinder thermostat. it has been used widely by BMW for emissions and performance purposes. In this case "MAP" is referring to the DME's (engine control module) internal MAP (mapping) which controls the thermostat. So you see in this case the terminology makes big difference.
I am going to attach what is called an I-P-O sheet which stands for inputs, processing and output. It shows every sensor input to the control module which in this case is the Siemens MS43 management system computer. It will show in a picture what im trying to explain in words.
Now that we can put that behind us please allow me to clear up the other issues as far as O2 voltage etc. I would never argue with you that checking o2 voltage is a bad thing or that it is inaccurate. I also am not trying to say that you need a bmw computer to measure O2 voltage. What I AM trying to say is that it really shouldnt be necessary. It is extremely rare to see any true voltage issues on the 02 circuit. Im not saying it isnt possible because it certainly is but it just almost never happens. What is much more common is either vacuum leaks, failed MAF's or MOST common is a dealer repgrogramming is needed because the o2 parameters are incorrect. There are at least 2 different programming bulletins posted by BMW addressing this. What I meant when I said you need a BMW fault code to know for sure is that the bulletins are listed under the BMW code not the OBD2 code.
So my personal advise to "447836......." would be to 1)check for vacuum leaks (check especially the intake air boot where the small part of the boot goes in to the throttle body, this is a very common leak on x5 3.0L)
If nothing is found then it is best to take the car to the dealer and have them run the faults and look at the BMW specific codes, compare them with any relevant service bulletins and also check the Adaptation values to get a true idea of what the management system is doing and what the MAF is inputting. As far as the MAP thermostat fault I would clear it and ignore it unless it returns in which case then the thermostat may need replacing or the circuit may need to be checked. Not everybody may agree with this but thats my advise and everyone here is entitled to give their own, including you The Cleaner.
I only hope to be helpful here Cleaner and I know that you are a veteran here and I am a NOOB but I certainly am no NOOB when it comes to BMW and BMW managemwent systems.
To the original poster please check that intake air boot, like I said its a very common failure.
http://216.93.207.213:8080/ipo.jpg
P.S The DISA valve is a electronically controlled flap in the intake manifold which changes the length of the intake runners depending on conditions in order to help with performance,emissions, and fuel economy. If you would like more technical information on it please PM me or email me and I'd be happy to send it to you.
Cheers my friend.
EDIT> also here is a portion of an actual BMW bulletin for reprogramming the O2 sensors on the MS43 management system. Im not saying this bulletin applies or will fix the problem but Im posting it so that you can see the BMW specific fault codes vs the OBD2 fault codes and why it is important to read the BMW faults.
http://216.93.207.213:8080/bulletin.doc