My 96 850 na is misfiring when i accelerate, and when in park or neutral the idle is either at 2000 rpm, or is jumping up and down every second betweek 1500 and 1800 rpm. This came out of nowhere after the car sat for around a month. What could cause this?

 

misfiring only during acceleration is always plug wires (ignition leads) or associated areas where high tension electricity could "leak" out.

I am going to argue that the high idle is a coincidence. I could certainly be wrong.