DELPHI - Is there a way to free an object created at runtime without getting 'Access Violation?'

this problem is driving me crazy, i have an edit box in which i write something. On event 'change' of edit box, a ListBox is created and filled by SQL query. It works as a hint box while writing.
When i hit enter on the item which i want to select, the listbox should 'free', but it continues to return me 'access violation'. Here the code:

procedure TFTimbra.EditCommessaKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
var
  X, Y, W: Integer;
  QSugg: TAdoQuery;
begin
  if not Assigned(Suggerimento) then
  begin
    Suggerimento := TListBox.Create(Self);
    Y := EditCommessa.Top + EditCommessa.Height;
    X := EditCommessa.Left;
    W := EditCommessa.Width;

    with Suggerimento do
    begin
      Top := Y;
      Left := X;
      Width := W;
      Height := 200;
      Parent := FTimbra;
      BorderStyle := bsNone;
      Font.Size := 14;
      Font.Style := [fsBold];
    end;
  end else
    Suggerimento.Clear;

  if Key = 40 then
    Suggerimento.SetFocus;

  QSugg := TAdoQuery.Create(nil);
  QSugg.ConnectionString := DMMain.DBConnection.ConnectionString;
  QSugg.SQL.Text := format('select Codice, Descrizione from Commesse where Descrizione like %s', 
    [quotedstr('%' + EditCommessa.Text + '%')]);
  QSugg.Open;

  while not QSugg.Eof do
  begin
    Suggerimento.Items.Add(QSugg.FieldByName('Descrizione').AsString);
    QSugg.Next;
  end;

  QSugg.Close;
  if Assigned(Suggerimento) then Suggerimento.OnKeyDown := SuggerimentoKeyDown;
end;

This is the first part, and this is the code that "should" free the listbox:

procedure TFTimbra.SuggerimentoKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Key = 13 then
  begin
    Commessa := Suggerimento.Items[Suggerimento.ItemIndex];
    EditCommessa.Text := Commessa;
    Suggerimento.Free;
  end;
end;

I think the problem is in the call of the OnKeyDown function.. Thank you in advance.

You can't destroy an object from one of that object's own event handlers. When the event handler returns, the code continues executing in the context of the object, which you just freed. And that typically leads to runtime errors like this.

Rather than use a dynamic lifetime for this list box control, create it in the traditional way, using the form designer. When you want it hidden, set Visible to False. When you want it to show, set Visible to True.