Hi,
If you have GPS problems with TomTom on the iPhone you might like to read "Some Initial comments on TomTom (UK) and a possible cure for bad GPS Reception" in the iPhone Accessories Forum.
https://forums.macrumors.com/threads/772135/
It worked for me but if it doesn't work for you my apologies for wasting your time.

If you have GPS problems with TomTom on the iPhone you might like to read "Some Initial comments on TomTom (UK) and a possible cure for bad GPS Reception" in the iPhone Accessories Forum.
https://forums.macrumors.com/threads/772135/
It worked for me but if it doesn't work for you my apologies for wasting your time.