Start with and Inspection 2 servive plus ALL fluid and rubber (hoses etc) change. CPS are prone to failure as are fuel pumps. Do the service and see what happens. Too expensive to change too much on spec.
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