Most of the links on Google are dead, but are not being removed because there is a Status 200 (OK) page being served as a 404 page. Instead of Status 404 (Bad Request).
Could you please update the 404 page to either serve correctly as a error page, or add a mod_rewrite rule to fix the bad links? Something like RewriteEngine On
RewriteBase /
RewriteRule ^?([A-Za-z0-9-_]+)=([A-Za-z0-9-_]+)$ /index.php?$1=$2
could possibly work, though untested.
Additionally adding <meta name="robots" content="noindex, noarchive" />
to your 404 will help robots.
If you can support PHP, or the page is served via PHP a simple http_response_code(404);
before any other headers are sent will correct the error page. Assuming it's not dynamically served by apache/nginx.