Filter Loop by Custom Field Value

How about this:

$my_query = new WP_Query(array(
                                'post_type'=> 'custom_type',
                                'post_status' => 'publish',
                                'meta_key' => 'my_custom_field',
                                'meta_value' => 'custom field value'
                              ));

if($my_query->have_posts()):
    while($my_query->have_posts()):$my_query->the_post();
        //All the post stuff here.
    endwhile;
endif;
wp_reset_postdata();

Check this out.