I have a 1992 Pontiac Bonneville with a 3.8L not supercharged. It has a rough idle yet it is fine when on the accelerator. Also it idles between 500-600rpm which seems low to me. After driving it for about 15 minutes the car will sputter and die. It usually will not start back up and even when it does it will idle but if i hit the gas it will sputter and die. It seems to only do this when i am stopped or at low rpm. The car remains inoperable until it has sat for a little while and will start up and run again for about 15 minutes. To my memory it has not done this if i am travelling at a higher speed. I have replaced the Idle Air Control, Throttle Positioning Sensor, Knock Sensor, Camshaft Position Sensor, and even removed my Catalytic Converter because i was getting a sulfur smell and thought maybe it was clogged and stalling the engine when it got hot. At this point i am at a loss and in need of direction. I am thoroughly convinced my idle issue and my stalling issue are tied together. It is NOT throwing an engine light and YES my engine like works. It could be a fuel issue but i am not that knowledgeable about the fuel system of a car. HELP ME PLEASE!!!