Why does my MBP kernal_task exceed 100% and drop wifi connection?

Several months ago my MBP started to occasionally become very slow while browsing the net to the point of being unusable. A restart would clear up the problem for a while ranging from a few days to weeks. After this happened a few times I started checking system monitor and discovered that the 'kernal_task' process was running at over 100%. Last week it started happening again after several weeks of normal operation only this time a restart did not clear the problem. After several restarts, I turned off WiFi and then it started fine but when I started WiFi, within 30 seconds, the kernal_task process went up over 100%. Today after being shut down for 24 hours, I started it up (WiFi turned off) and then once it was up turned WiFi on and its now been running normally for a couple of hours.