Both of those are VERY unlikely to be the cause of his car stalling. Like someone said, a vacuum leak is possible. I would also look into the IAC (Idle Air Control). If the engine throws a check engine light, take it to AutoZone (i think?) and they will check the code for you for free.

Also, I'm pretty certain the Concorde's didn't have a 3.6 litre V6, I think it's a 3.5. Not that it matters.

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