Tune ups and maybe a compression test just to scare you! Run premium fuel - the EMU will give you best mpg after a time. Also try the shorting the CAR's battery terminals out for 20min. It will clear historic faults from the EMU. (Note: Do not short out the battery - only the car's terminals with the battery disconnected)
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