Hi Tim,
sorry to hear your still having ECU problems, as I assume the 'clocks' installation didn't work? What a shame, I thought we'd cracked it.
I have searched many times and never found anyone willing to modify a M52 ECU to remove the immobiliser. (If anyone knows, the're not telling !!)
I have considered two other options but not tested either....
1) get an M50 manifold, injectors ECU and engine wiring loom. No idea if it would work and the twin Vanos would certainly not work correctly.
2) Use an aftermarket ECU. I spent quite a lot of time researching all the options I could find but only a very few can properly manage the BMW twin Vanos. The best match (on paper) is a DTA Fast S 100 pro.
http://www.dtafast.co.uk/S_100_PRO.htm
They actually have wiring diagram for an M52 and I'm sure it will work. However, you're talking a £1k for the box plus a few hundred to get it mapped properly.
...sorry not much help...
...peter