Agregar custom meta data al buscador de WordPress

functions.php

<?php 
function custom_search_query( $query ) {
  $custom_fields = array(
    //agregamos los valores de los custom meta data
		"_post_title",
		"custom_meta1",
		"custom_meta2"
	);
	$searchterm = $query->query_vars['s'];
	$query->query_vars['s'] = "";
	if ($searchterm != "") {
		$meta_query = array('relation' => 'OR');
		foreach($custom_fields as $cf) {
			array_push($meta_query, array(
			'key' => $cf,
			'value' => $searchterm,
			'compare' => 'LIKE'
			));
		}
		$query->set("meta_query", $meta_query);
	};
}
add_filter( "pre_get_posts", "custom_search_query");
add_action( "save_post", "add_title_custom_field");

function add_title_custom_field($postid){
	update_post_meta($postid, "_post_title", $_POST["post_title"]);
}
?>