Looking for some help on this one, got my Z1 install done and noticed it has been acting a bit weird lately. Unit was used but in good condition.

I did get the speed sense wire connected and the GPS antenna mounted in the stock location (shows good reception from most satellites at all times)

As I'm driving around, the vehicle position will be off by as much as a block or two, and then will jump to the correct position every couple minutes. I assume that this means the GPS can find the location correctly but that the accelerometer is doing weird things to the position in the meantime. One thing I have noticed is that when coming to a stop sign, whenever I hit the brakes it appears that the vehicle position is actually going backwards.

Not sure what to do about this, I attempted to reset the accelerometer calibration, evidently it is supposed to get better as I drive around.

Not sure if I've done something incorrectly or if I just need to calibrate correctly. Any help is appreciated.

Maybe moving your GPS antenna to another location if it is not on the roof of the car might help. Also, make sure your VSS wire is installed properly...

Sounds like you have the wrong VSS wire. It updating every so often it the GPS pinging. The radio thinks your going slower than you actually are.

It could very well be the antenna getting infrequent fixes and the unit guessing, based on speed and motion sensor, which way you're going. It's like going through a loooong tunnel, when you come out the other end the unit will make a correction based on the new satellite determined position.

If you have the antenna inside the car, temporarely put it through the window on the roof to see if that takes care of the problem. Mine is under the dash and workes perfectly since slightly moving it a couple of times.