sorry to dig up an older thread, but mine is doing something similar. It seems like the temp will climb normally, then it will drop to 0 and then back up, back down..etc. I am getting my reading from an Edge Insight CTS. It did not do this at first, but only recently. The way it is acting, it seems like a ground issue as well. I will be checking this soon. Thanks for posting up that info and for reporting back that you fixed it. Were you able to fix the end in the plug that was messed up?
Brian