Where did it sit? Could animals have done a number on the wiring? Is it the original wiring harness?

Next train of thought, massive air leak from deteriorated turbos hose (usually happens on the bottom of the hose where oil pools...and you can't see it).

Finally, if you exhaust has an inspection port, remove it and see if the car runs better...the "Cat Ball" could be at fault but that rarely happens suddenly.