I have a 2003 Hyundai Accent with 166K on it. A couple of weeks ago I drove it and for an hour and parked, then after several hours I tried to start it and it wouldn't start. I had it looked at and found out that the fuel pump was not buzzing. I replaced it, it started and I drove it for a couple days then it died and didn't start again. It cranked but wouldn't start. To get it to start again, I had to spray starter fluid and then was able to drive it home. A couple of days later, while I was idling at a traffic light, it died. The engine cranked but it wouldn't start. I used starter fluid again and got it home. Once I use starter fluid it runs fine, like nothing is wrong with it. There is no fault code present. I replaced the fuel relay, fuel pressure regulator, ECU, fuel filter and spark plugs but I still have the same issue. What else do I need to replace? The car will start sometimes and sometimes it won't. Sometimes it will start fine without starter fluid and then other times when it randomly shuts off, I have to use it. I was going to replace the crank positioning sensor but since the car starts with starter fluid I think it may have something to do with the fuel.

Does anyone know what could be causing this. Any suggestions would be helpful.