1992 Other Volkswagen Models engine stalling

Well all vehicles have some sort of idle control. I'm not familiar with your particular engine, but I am guessing throttle body injection. By '92 it would have an idle control that would be variable. The question is if it is something the computer is supposed to do or if it is manual. The fact that the engine stalls after it has been warmed tells me that it is computer controlled because that means the engine idles itself up until it is warm. You could try starting the engine and watching the throttle cable until the engine idles down so you can locate where the idle control is and how it works. I know some engines have a minimum idle screw you can adjust where the throttle cable meets the throttle plate. This would patch your problem temporary, but I think you may want to look into it some more.