The first one is correct. The second one sounds really unnatural and although I'm not sure if it is grammatically correct or incorrect, I am positive it is wrong ... use the first!

If I had a lot of money, I would buy a new car.

1) If I had a lot of money, I would buy a new car > correct , but you used the "past tense" ( 2nd conditional to mean that it is just something you imagine and unlikely to happen, . Unlikely you will have the money)). 2) If I have a lot of money, I will buy a new car > correct . You are using the present tense ( 1st conditional to mean that this is exactly what you will do if you have money , and its possible that you may have it in the future.

=> If i had a lot of money, i would buy a new car.

If I had a lot of money, I would buy a new car & If I have a lot of money, I will buy a new car. Nothing else is possible, despite what you may hear on TV, in film and amongst native speakers.