Engine trouble / Story

Actually I am not sure if It is engine trouble. Anyways, I am 17 years old, I drive an oldsmobile cutlass supreme '91. My father is convinced it is an excellent car and that it would be worth our time to keep putting money into it. So far around 4k ( think of what that could have bought me :() Anyways back to topic. My car recently had a new engine put in by a bunch of fucking hobos at this repair shop in town. So anyways, I finnally get my car (it will be there monday promise, oh sorry, tuesday,oh sorry wensday, oh sorry friday, oh sorry monday). Anyways, they finnaly got it back to me and claimed it was in great shape I would love it. Well, I hopped in my car to go do a project for my friend whos a senior and need help with computer stuff so we go to drive away from the dealer. Well in order to cross the highway we kinda have to drive the wrong way on the access road and it wasnt really that bad but I had no light, so I went to floor it and what happens? You guessed it nothing, I noticed the car infact was not on. I proceeded to turn the car back on, it started up. Oh, I looked at the gas gage, the fuckers used all my gas (i had 0 gas actually including extra). So, I put the car and park get out go to the guys be like hey I have no gas. So they let some scary hobo get in the car with my friend (my friend still had the car door open) and the hobo just takes off squeeling to the gas station. And they are all standing around laughing about how funny it is that the guy is driving crazy in my car. So I get more gas and he comes back blah blah, I get in my car to drive I drive for a while doo de dooo, la la la driving back home to do project la la la, and what happens as I goto turn? I CANT! The car turned off agian, so good bye power steering, put the car in neutral turn it on keep going, happens agian, HAPPENS AGIAN, HAPPENS agian. I cant say that slamming the gas effects it, nor can I say that sitting idle causes it to turn off. I dont know why it turns off, and cannot begin to understand why it is doin it. Any ideas? At all?