All these problems appear to be the fault of a vehicle that was stored, undriven.
A friend bought a Chevy Lumina minivan, that exhibits much of the same problems. Stumbling, poor idle, too fast or too slow, misfire etc.
He wanted a car that didn't have to be emission tested and nice shape for it's age.
It turned out to be, the car was traded by a lady who got the car from her late father. It wasn't driven for like, three years. Newer vehicles, just don't age very well.