Have you run a pressure check and changed the fuel filter? Looking at what the PO's did to the dash I'm amazed it's even running! I hope you were paid to take it away. I've seen parts cars better than that. Good to see a bloke who loves a chalenge. I saw a AFM fix on another forum (can't remember which) for this style of meter. You do have to have all the bits installed and working before the engine will run properly and it's a pain to establish what the ECM is missing out on. It is always a great feeling to drive your own rebuild. Goog luck.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i