I suggest taking stock injectors to FI shop who can do an off car clean, flow and spray pattern test. Has worked very well for me in the past. I have heard horror stories about tank aditives that 'clean' injectors.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i