I have a similar problem on my Aus 04 X5 with retro fitted Mk4. My car alrady had the factory fitted screen, tv tuner & nav wiring. I just fitted the Mk4 & a BMW GPS antenna.

My position is laggy, always about 50M behind and it never catches up even when stationary, all my sensors seem to work and it accurately plots my position in tunnels.

My position is always on a road and never strays off road on top of a house, etc.

I imagine that what I have is normal operation for a Mk4?

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PC

04 X5 3.0D
Sydney, Australia