I have a 91 Camaro RS V8. It has a lot of miles on it but has been very well taken care of since it was driven off the show room floor. I let someone drive it and now it's running really bad. First thing I noticed was it wanting to stall out at every stop and it was running real rough, the day before it was purring like a kitten. So I've replaced the MAP sensor, the air intake valve, the o2 censor, and it still is running rich but it did make a little improvement. I had just put new plugs in but was told I should have them cleaned and checked again because of all the resent problems.
When I took it to the shop to have the o2 censor replaced the mechanic told me I was leaking coolant which when I took it there it wasn't leaking at all. Not to mention I always put orange coolant in my car and when the mechanic showed me where it was leaking I saw green coolant under my car. So thinking these guys were doing me wrong I took the car home and it is indeed leaking coolant.
There was no pressure in the top radiator hose so I replaced the thermostat thinking it was stuck closed. At first it seemed to fix the over heating problem but it is not consistent. When I start the car black smoke come out of the tail pipes and you can see black sute on the ground and it smells like gas. My question is what is my next move? Go easy on me I'm just a girl that is here to learn. I love my Car!

 

How long did that someone borrow your car for? Did they fill your gas tank and perhaps got crappy gas? Or maybe accidentally put in diesel, yes it's happened (not to me)! Black smoke out of the exhaust usually means you're running rich. Try to flash the codes, even if your check engine light isn't on. Here's how: https://camaroforums.com/forum/82-92...d-codes-20385/
Come back with the codes if you have any, and we can help you make sense of it.
As far as the coolant leak, that's going to be hard to guide you there without not knowing where it's coming from, it could be a number of things.