High CPU useage when board is set to active

[patracy]

A little background about a month ago (35 days) we saw this behavior. Tried cycling apache, that only helped for a moment or two. Ended up simply rebooting the server and things seemed to be fine after that. The past few days I had noticed high useage. Until yesterday when things slowed to a crawl. To the point that it took several times to even SSH into the server. Utilization in the 200's. Stopped httpd, things behave. Turned it back on, cpu utilization rockets. So I started to try to pick apart all the "bolt ons" to the forum. Disabled the openx ads, a few things on the sidebars. Problem repeated. I haven't added any plugins in quite some time, so I disabled all of them. Problem is still there with the forum active. Now, flip the forum to off (mods/admins can view only), and it's fine. It's been fine all night like that.

There's a few things that need to be updated. I did go ahead and update httpd. But that seems to have no effect. There's still mysql and php that need updates. (I know vB needs those at least from the list) I guess I'll update them.

Just at a loss what the cause is, and why it "resolved" itself last month from a reboot.

System info:
Centos 6.5 on VM
2 CPU 3ghz
8gb ram, 6.5gb in use currently in "offline" mode.
MySql 5.1.73
PHP 5.3.3
Apache/2.2.15
vB 4.2.1 PL1 with a few of the CP patched files from 4.2.3
Running zbblock as well.