I know you like the 99 model Seville. (That was a nice body style) But I'd pass on that car if I were you.
There's waaay too many possible causes to a car's engine dieing at idle. This could be anything in the ignition system, fuel system, P.C.M, or even something mechanical like low oil pressure causing the fuel pump's relay to trip.
If the " check engine" light is on, you could have the computer scanned for codes. This'll give you a place to start. But those Northstar engines are notorious for failure, and I'd run the other way if I were you!
If you absolutely MUST have a seville of that body style, look for a V6.