I was having a problem it was reading -40 I rewired it all after I figured the sensor wasnt bad It worked right wired off the harness

I rewired my temp sensor I didnt connect wires just cut the coating of the end of the wires and held them together doing that I get a acurate temp

If I then use lock tabs or butt connectores I get a -2 reading

 

sounds like you have a bad connection, ive never had a problem with butt connectors and shrink wrap.

 

Sometimes solder is the only way to go.