My GPS works great!
I can get a lock in about 10 seconds and to within 10 metres or less of my position.
However, if you remove both data and wi-fi from the equation, the lock can take up to 20 minutes or more and the accuracy is about 500 metres.
This is to be expected because of the way that GPS works in mobile/cell phones to ascertain your position.
For more details about this, see here:-
How Does GPS Work In Cell Phones?
Hope this helps.