o2 sensor problem would give a trouble code amd it would just run poorly, not stall. Stalling like you have is usually a result of a weak ignition module(common),and possibly a crank sensor. The module will NOT show a trouble code and crank sensor may or may not. Your digital egr valve could be acting up bu that usually results in a badly running car and will also give a trouble code. My advice is to have the module checked out. Yours is under the coils and the coils and module are removed as one part, three #10 bolts should be holding it on. Pretty sure yours is at the top of the motor though, unlike our old 91, which was in hard place to reach. Take the module and have it tested. Although they can sometimes fool the test equipment it should show as weak. Replace it if so. What happens is that they will act up when warm.