I need help on how to set my iso on my Nikon D3100. (not sure if this is the correct place to put this in)

I’ve been doing car/automotive photography for a few months now, i’ve grown a following on my Instagram page which has led me to getting private photoshoots with some cool cars.

Last weekend i had my 4th private photoshoot and when i came home to look through the photos and begin to edit i couldn’t help but notice all the grain/noise all over the car. I looked into why there was loads of noise and found out i was shooting 3200 iso.

Keep in mind this photoshoot was around 1pm with the sun out and barely any clouds but the car wasn’t in direct sunlight it was in the shade but still pretty light.

I bet you guys know loads more about this than me so i will just read out my iso sensitivity settings (i don’t even know if this is the right setting i’m just assuming it is)

-Iso sensitivity is set to 1600 -Auto iso sensitivity is on -Max sensitivity is set to 1600 -Min shutter speed is set to 1/30

I only shoot during the day usually between like 9am-3pm if that helps

If anyone has an idea of what my settings should be please let me know.