My 2000 ML 430 starts just fine. Then it will die a few miles down the road - basically when the engine gets warm. It kranks but won't start. If you wait 30 min to an hour it will start back up and go a few more miles.

I had it diagnosed this morning at a local shop and they tell me I need a new EGR and that 2 cylinders are not firing.

Does anyone know which of these two issues is causing my problem? The shop (of course) doesn't know. Which one do I do first? Can I replace only 2 of the spark plugs? What exactly is an EGR anyway?

Help!!!