I kind of have a similar problem, but my Z1 one with Z3 image is on crack. I will be driving, and it will have my correct location, then all of a sudden I can be on the highway, and it will tell me to turn around, then it will keep giving me directions properly. Then sometimes I will be in my neighbor hood, it will have me at the right place, then will tell me to run down the wrong street and when im 3 blocks from my house will tell me I arrived at my destination.
My antenna is mounted outside my car on the roof, so its getting the best signal it can get.
Anybody have any thought