99 Civic si b16a2 with a P30 running on OBD1 with some bolt0ons. inatake headers etc.

I was wondering what could be the problem that when its really hot outside the car has a hard time starting but when its in the shade or its not too hot outside it starts up fine, i live in 100+ degree weather in AZ. when the car is in the shade and i start it it will start and catch idle after a bit but when its in the sun itll start and just turn off. idle wont catch. kinda weird if you ask me.

 

Possible main relay

 

Like HPH says,
if it has a hard time turning over during hot weather, it could possibly be the main relay,
Although if the car is turning over during the hot conditions, but having a hard time firing, I would suggest fuel supply (Fuel pressure regulator)

 

Do some basic diagnostics so you don't have to guess.

CEL codes?

ONLY when the engine won't start:

Does the fuel pump prime?

Bright white spark at all 4 plugs?

 

No codes at all, and itll start but then turn off, i have to keep the rpm's up in order for them to finally catch up a minute later.

fuel pump does prime and id need to check on the spark

and it can be hot as hell outside but if the car is in the shade usually itll start right up but i drive about 5 minutes to the gym and have to leave the car in direct sun light when i come out and try to turn it on it does this.