Hello and good evening, when it starts back up will it maintain running? And does it stall under cruise or when you slow down?
Your JA Expert,
Find out if they cleaned the Idle Air Control motor. It's possible and probable that they did not clean that component. What can happen is the IAC motor can close during cruise, and get stuck in the dirt that builds up in the housing. When you come to a stop the pintle may get stuck in the dirt, causing the stall. Then it frees up and is able to maintain idle. Since the plate was dirty enough to roughen up your idle, it's very possible that the IAC motor and housing are equally dirty, since they are related by location.
If the car does not stall again, the module could have been your problem. Generally the stalling due to a failed ignition module, would be followed up by a no start until the car cooled off. Another possibility is that the computer relearned it's new idle settings which can happen as well. See what happens over a period of time. If the stalling returns, let me know and we'll see if we can narrow it down. I'm here for you if you need me, so don't hesitate to reach out to me.
I feel better about your actions then. That fits. I think you fixed it then. Dealing with it while it still won't start is the way to fix it with confidence. Don't hesitate to let me know if something crops up. I don't think it will. Those Riveras are beautiful cars, enjoy it.