rirotary

So i bought this nice rx7 fc for a great price 700.... then i found out the guy pulled a fast one because the coolant seal went! what a *** right?? but i have been driving it and now randomly when i take a quick trip to somewhere turn the car off then get back to it...... it doesnt start! im thinking maybe loose wiring? but then i tighten the wires to my battery then when i start it up sounds like it wants to just die. So i press on the gas to make sure it doesnt die on me. So help me out because i dont want it to die on me when im driving it happen once already!