1989 Oldsmobile Cutlass car keeps turning off

I have a 89' Ciera Cutlass 3.3L the car had been running fine till last week. The car just turned off on me when I was at a stop light. So I parked turned it back on and pulled off to the side and it turned off again but all my lights were still on. The car kept turning off when id start it, it would stay started for about one minute and turn right back off. I was able to get it home and my brother worked on it, the radiator fan wasn't turning on so he ended up replacing the coolant temperature sensor, the motor to the fan and relay, we let the car run for 20 minutes and it was running fine even drove it around the block and it drove fine. However my brother also raised the Idol on the car even though it is a fuel injected engine. The car drove well that day and the next day I started my car and the engine revved three times by itself and turned off, when I turned it back on my service engine light was on and my speedometer stopped working. Drove the car to auto zone they couldn't help cuz the car is too old. Started the car agaim and my light was off and speedometer was working again. Tried to hurry home and it turned off again, had to leave it there I don't want to try to drive it because I dont know what's wrong with it.


What could be causing my car to turn off like that and what won't allow it to stay on?