I have a spare complete engine harness. I examined the back of the connector carefully it does not look like dirt can get to the front where the female pins are. This would make the solution link posted above useless because it only seals the back of the connector not the front. Has anyone completely dissected it? It is a very nice write up however.I think I mentioned this before. But if Kburger is having repeated problems with his M52TU throttle body (used only in '99 & '00), and has already tried replacing it with a replacement, it is likely not his throttle body, but the wiring in the stupid round 10-pin connector on the harness. The back of that connector, and its pins/wirings is open to the elements in the air flow around the engine block and easily degrades, causing tiny changes in millivolts sent/received between DME and throttle body (aka MDK), throwing the car into limp mode.
I have replaced the throttle body on my M52TU e39 six or seven times.
Here is a solution:
Diagnosing electronic throttle body faults and replacing its connector plug on 99-00 BMW 5 series.www.frankies-bmw.com
You could also try a used engine harness, but it will soon have the same problem. Several years ago, I looked into a new Genuine harness...according to my dealer parts counter, it had to be ordered from Germany and it was $750.
I haven't fixed my car yet..its in storage, but one idea I have, is to get the parts referred to in the link above, find a used harness - make sure its the correct one..year/model/trans, have the repair done professionally by an electronics specialist (I suck at wiring/soldering) and replace the harness. This will minimize down time.