When heating with the torch, you want to get the housing to glow bright orange. And keep it at that temperature for atleast 2-3 minutes. Make sure you get the ENTIRE housing, NOT the entire sensor, nice and hot. Then, just to make sure you don't shock the metal, give it a minute or two. It will actually cool rather quickly. If it sizzles when you spray the non-chlorinated brake cleaner onto the O2 sensor, you should wait a little longer. Do this atleast 2 times, preferably 3-4.

The first time you do it, you won't believe just how much gunk comes out in the brake cleaner. By the third and fourth time, the brake cleaner should come out clean.