Stalls In Park, Idles In Gear

Would like to know why my 93 GT will stall while it is in Park, but will idle fine once I shift it into any drive gear. I noticed this problem immediately after I had an issue while driving one morning where my positive battery cable somehow worked its way off of the battery and killed all power and the engine while I was driving it. I found the cable off and put it back on. Ever since this incident, the car will not maintain an idle unless it is in gear. Any advice will be greatly appreciated. Thanks in advance.

Thanks jrichker. I drove it for a continuous 15 minutes and it did improve the idle, but still not as good as it was before the issue. But it definitely has improved. Perhaps 30 minutes should do it. Thanks again.