You can keep your car in for 2 years at a time (renewable). However you have to have residency and proof that you are retired.If I remember correctly it costs about 935TL to keep the car in for 2 years. You also have to deposit a rather large amount of money in the bank that has to remain untouched. (the bank then sends a letter to the Turkish government stating that the money is in the account.)This letter is photocopied and is sent every year as long as your car is in the country.(The bank will charge you a fee for this....usually 650TL per year.)
Personally, having imported our car I can say that it isn't worth the money.