- This is not the correct way to write this. It would make sense if it was "I am going to have my car fixed." However, the word "have" is present tense. That means you are currently having your car being fixed.
2. I had my car fixed.
- This is the correct way to write this. The word "had" is past tense. That means you already fixed your car.
Explanation:
Remember that "have" is a helping verb, and "had" is the past participle. "Have" is a present form while "had" is the past form.
