[ecfisa]

Hola Enan0.

Fijate si así te sirve:

Código Delphi [-]
procedure TForm1.EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
var
  Msg: TMsg;
begin
  with ComboBox1 do
  begin
    case Key of
      VK_RETURN:begin
                  TEdit(Sender).Text:= Items[ItemIndex];
                  PeekMessage(Msg,0,WM_CHAR,WM_CHAR,PM_REMOVE); //quitar beep
                end;
      VK_DOWN: if ItemIndex < Items.Count-1 then
                 ItemIndex:= ItemIndex + 1;
      VK_UP: if ItemIndex > 0 then
                ItemIndex:= ItemIndex - 1;
    end;
  end;
end;

Saludos.