1 Guilherme
2 Alejandro
3 Thiago

da1.Fill(dt1);
BindingSource src = new BindingSource();
src.DataSource = dt1;
comboBox1.DataSource = src;
comboBox1.ValueMember = "ntj_id";
comboBox1.DisplayMember = "ntj_descricao";

int abre = comboBox1.FindString("Alejandro");
comboBox1.SelectedItem  = abre;

comboBox1.SelectedIndex = abre;