I am having a simular random stall problem with my 99 4-cyl, auto Mystique. however, my CEL was not on. It had a poor idle problem as well and sputtered under moderate acceleration. I tuned it up, plugs, plug wires, fuel filter, and fuel injector cleaner. Spent a good bit of time under the hood checking for bad vacuum hoses. I also checked and cleaned the battery terminals. And still experienced the same problems. I replaced the IAC valve and the idle problem was fixed. However, it still stalled and sputtered.
I finally gave up and handed it over to a good local mechanic that I have used in the past, he used to work at a ford dealer before he opened his own shop. He seems to think it is a electrical problem in the wiring somewhere and has been trying to track it down.
You may have an electrical problem as well. Just thought I would mention it.
