How to assign a custom post title to be the post ID?

Question

Is it possible to assign a custom post title name to the post ID upon submitting an ACF form? I'm trying to do this because I don't use the custom post title, instead I just want it to be the post ID. I'm using the "twentythirteen" template.

Here's what I have to assign the post title from ACF fields in the functions.php:

function auto_title_insert( $value ) {
  if ( !$value ) :
    $value = $_POST['fields']['field_538626f57e84c'].' '.$_POST['fields']['field_538627ffeccb0'].' '.$_POST['fields']['field_53863a5c7502b'].' '.$_POST['fields']['fields[field_53a9bb09f82ba]'];
    return $value;
  endif;
  return $value;
}
add_filter( 'title_save_pre', 'auto_title_insert' );

The problem is, the title doesn't change when the custom post type is updated

Here's what I have for when the post is updated:

function my_acf_update_value( $value, $post_id, $field ) {
    global $_POST;
    // vars
    $new_title = get_field('make', $post_id) . ' ' . $value;
    $new_slug = sanitize_title( $new_title );
    // update post
    // http://codex.wordpress.org/Function_Reference/wp_update_post
      $my_post = array(
      'ID'              => $post_id,
      'post_title'      => $new_title,
      'post_name'       => $new_slug
  );
// Update the post into the database
  wp_update_post( $my_post );   
}
add_filter('acf/update_value/make=make', 'my_acf_update_value', 10, 3);

The problem is I can only get it to work for one custom field instead of updating multiple fields

Here's what I have to make the title name the time stamp:

function auto_title_insert( $value ) {
  if ( !$value ) :
    $value = '['.get_the_date('d/m/Y @ H:i:s').']';
  endif;
  return $value;
}
add_filter( 'title_save_pre', 'auto_title_insert' );

That's ok, but I really want the post ID for organization

Answer 1

You could set it to the post ID when the post is first created via the default_title filter.

function wpd_default_title_filter( $post_title, $post ) {
    if( 'your_post_type' == $post->post_type ) {
        return $post->ID;
    }
    return $post_title;
}
add_filter( 'default_title', 'wpd_default_title_filter', 20, 2 );