My 99 Hyundai Elantra will be running fine and die out of nowhere. What could cause the problem?

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Question moved to model category.

Clean throttle body and MAF.

If that doesn't work, you need an auto electrician with a pro grade scan tool computer to diagnose the electronics.

Do the injectors have power to them and a ground pulse command signal ?

Have you had the charging system tested by a shop ? Is the alternator charging the battery ?

My friend had this problem with her Hyundai 2003 Sante Fe...just dying out. And I did some research for her. There was one particular forum, where I Googled the make and model, year of the vehicle that came up where a few people had this problem. And the problem isn't picked up by the dearler's computer test. The part was the EGR solenoid control valve. Maybe that's a place to start?

sir, your car's wiring get short ..pls check its main head beam relay...

check fuel presure and replace fuel pump if needed

best to put it on the diagnostics, it could be the auto chock that kicks in it just thinks the engine is cold,

When gasoline sits for that length of time it turns into a varnish like substance. It gets the consistancy of something like real sticky warm creamy peanut butter. (basically turns to thick sticky muck). Which plugs the pick-up screen on the fuel pump, the fuel injectors and can even plug the fuel lines. Fuel injectors are designed to "spray" the fuel into the intake in a very fine mist. I believe the reason it starts then dies is because even though the injectors are plugged they will "drip" fuel because of the pressure that fuel injection works on. The "drip" is just enough to fire the engine and then die.
What you can do to confirm that the problem is actually fuel related is, using a can of carbuerater cleaner (in a spray can) start the engine while spraying into the air intake. If the engine keeps running as long as you keep spraying, the problem IS fuel related. If the engine doesn't stay running when sprayed. Then the problem is NOT fuel related. I don't recommend using "brake clean" to do this because some brands of "brake clean" are non-flammable. I hope I wrote this so that you understand what to do. Good luck.

Try replacing your fuel pump and check for possible dirts in your fuel system.

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your charging system is not working,so your car is working only on batt. power,when batt.gets weak car will cut off! good chance alter nator is defective! check alt.elect. connections at alt,if con.are good its alt.