I have 1986 Nissan sentra, the car runs good most of the time.

Your problem can be caused by numerous things. I would rule out the simple things like spark plugs, wires, distributor cap, Ignition rotor, and a bad starter. It might be a good idea to replace all of these things if they have not been replaced in the last 2-3 years (all of the parts listed will run around 150-200 with the starter, if its not the starter then the other items are around 50). Also check your entire fuel system including any injectors and clean the throttle body. If your fuel system and spark plugs check out it can be hell trying to find this problem. Issues can be Bad relays (electrical related) or any number of sensors may have gone bad and the car is confused on what to do. I would have this taken to a local mechanic or if you have the tools to check for issues via the computer. It will likely have a code that you can either google search or get from a manual what it means and what needs to be changed. Its ahrd to diagnose an issue liek this without actually seeing the car because like i said it can be 20 different things