  The one-dimensional (1D) $t$-$J$ Holstein model is studied by exact
diagonalization of finite rings using a variational approximation for the
phonon states. Due to renormalization effects induced by the phonons, for
intermediate electron-phonon coupling, the phase separation (PS) boundary, and
with it the region of dominating superconducting fluctuations is shifted
substantially to smaller values of $J/t$ as compared to the pure $t$-$J$ model.
Superconducting correlations are weakened through charge density wave
interactions mediated by the phonons. Possible consequences for the high $T_c$
oxides are discussed.
