The 55mph stall?

I have an 89 Buick Park Ave. It will stall going down the road. Not much warning somtimes a sputter but more like the key was turned off. I can slide it into netrual and restart sometimes it is fine for miles and other times it repeats. The fuel filter is new. It is showing a check engine light and i was trying to find the plug to check the code. It is no where to be found. Any help would be awesome...Thanks

The connector is in the center of the dash underside (just below the ash tray.)