1st and formost get a good battery in it( you would be suprised what that can cause)
Unless it's sitting codes, anything is a guess.

Like mentioned above all are known issues. I have run into a couple over the years where the engine harness rubbed thru and was shorting out against the edge of master cylinder casting.

lower wire harness to the crank sensor( down low and on the back side of the engine on the old ones) Especially if the head gasket is or has been leaking oil.