The iterative difference dedicated configuration interaction (IDDCI) method, recently proposed for calculating excited electronic states, is tested in systems where the core valence correlation plays an important role. The calculated ionization potential, electron affinity, and electronic transition energies of K and Rb agree within 0.1 eV with experimental values. The three lowest Sigma(+) potential curves of KH and RbH and the six lowest states Sigma(g)(+), Sigma(u)(+), and Pi(u) of K-2 are calculated with the same accuracy.