Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
Importing Your Car Tax-Free
Vehicle tax (ISV) in Portugal can be extremely high. However, new residents can import one car tax-free if they have owned it for at least 6 months in their country of origin before moving.
You must start this process at Customs (Alfândega) within 12 months of getting your residency. Be warned: if you sell the car within the first 12 months of importing it, you will have to pay the full tax retroactively.