Sent CPU/GPU plimit notification? High CPU

I've had a bunch of these errors showing up for a while now. Randomly my mac's CPU spikes, and it crawls to a slow halt.

I ran the hardware diagnostic tool, and it came up with an error which I believe is related to temperature 4SNS/1/00000 or something similar.

If i check the system console, I get the following messages every 15 seconds or so:

04/03/2014 15:15:41.000 kernel[0]: IOPPF: Sent cpu-plimit-notification last value 8 (rounded time weighted average 7)

04/03/2014 15:15:41.000 kernel[0]: IOPPF: Sent gpu-external-plimit-notification last value 0 (rounded time weighted average 0)

Do you think the two are related? I've tried googling the console messages, but i've not found a great deal.

Thanks.