Firstly the 90/180 day rule is across the EU and not to a specific EU country. So if I travel by car through France and Spain to get to Portugal the time I spend in France and Spain forms part of the 90 days.
So where I have a concern is that I may have residency in Portugal where I stay for over 90 days and all is good but, when I return in the car through Spain and France they may well view me as having been in the EU for over 90 days and of course, when I get to the hard EU border at Calais how would they know when I entered and left Portugal and would they still include that time since Portugal is part of the EU.
This rule has been used for many years by non-EU residents so I would be interested to hear their experience of this.
Paul, Tavira