The power commander can be unplugged. There'll be 4 plugs, once disconnected you'll see the plugs will go back together as the PC only joins into the Oxy sensor and injectors if I remember right. If there's no difference you can plug it back in, the map will still be on there. If you get the tank up to change the plugs you can get a good look around link pipes, plugs and joints. Been hearing of fake NGK plugs being sold on eBay, don't know how true that is.
Buck and Freds suggestions are a low cost tries so worth a go but it sounds like a Vac leak to me, or possible map sensor.