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.
There are several things you need to do. The most important is to delete and replace all of the core Wordpress files. I've been running in to a lot of issues where the files are placed directly in the wp-include directory. The other issue is to scan through all of the theme and plugin files to manually remove the infection. That sounds labor intensive, but it's not as bad as you would think. I would also check the database for hacked and phantom pages. Over the last few weeks I've seen several instances where the injected code was written directly in to the database. In addition run an automated anti-malware scan to make sure nothing was missed.
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 10+ years development experience with Wordpress. 15+ 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