Cold start injector usually in center square bit of inlet manifold. While you are at it get ALL injectors rig cleaned and tested. Air in system should be flowed out fairly fast by circulating fuel and end up in the gas (petrol) tank.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 White and 1 Light Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i