i have looked in the search and can't find anyone with this problem. when the car is started the idle moves up and down almost hitting zero, but the car doesn't die. but when i am at a red light the idle would do teh same thing and it has died on me and i would have to restart the car. what could cause this? dirty fuel injectors, computer?

 

Let me take a load off your chest by saying right away that I don't know .
In all fairness, nobody else here would know either.

Take it to a mechanic and let them figure it out. Then get a second opinion.

You may also want to mention the make, year, model of your vehicle, mileage, what kind of service / maintenance you have or have not done, etc.
You've described the symptoms, but left so many variables out that I doubt you'll receive any useful info, as is.

It may be EGR valve, O2 sensor, spark plugs, etc., etc., etc.

 

fuel pump on its way out? bad fuel pump ECU? it could be a number of things.

 

Try maybe a complete fuel system cleaner to clear up dirty fuel lines.