This is one of the things I specialize in. I spend a lot of time, on an almost daily basis, repairing infected/malfunctioning Wordpress installs.
I can run a scan on the site to make sure all of the files are clean. I will also manually replace all of the core Wordpress files and plugins if needed. In addition I'll check the database to make sure nothing has been injected in to any of the posts. I have seen several instances over the last several months where the site is clean but the database is infected.
There are a few other things to look for but it normally takes a few hours, or less, to search out and fix the problem.
I'll also make sure your site is secure when I'm done.
I have 12+ years development experience with Wordpress. 17+ years development experience with PHP, MySQL and Javascript. Wrote my first web page way back in 1995. I have the experience you need to get this done efficiently and quickly. I can definitely fix this for you.
Thanks,
-Dave