I have the same year e30 that I just bought too. It idles rough and spits black smoke too. Before even driving it, the very least to do is to get a new O2 sensor and clean/new injectors. Fuel filter, stop any fluid leaks with new gaskets. As suggested above, cap, rotor, wires and coil. Replace spark plugs after all that is done to avoid fouling the new ones. Any other suggestions?
Check codes and solve those problems.
check belts for wear.
BigEvil, any idea why the platimum plugs aren't suited for the e30? Brands?
I got Champion iridium because I have a job there, and their logo is cool.