https://www.mediawiki.org/w/api.php?action=query&list=search&srsearch=A+B
Asking for Lucene seemed to work more consistently. One of the errors:
PHP fatal error in /usr/local/apache/common-local/w/api.php line 3:
require() [<a href='function.require'>function.require</a>]: Failed opening required '/usr/local/apache/common-local/php-1.23wmf18/api.php' (include_path='.:/usr/share/php:/usr/local/apache/common/php')
Version: unspecified
Severity: normal