91 240sx : drop in power on stock KA

[Zyphar]

I got a sudden problem. When I was driving to work Thursday, I suddenly got a loss in power without any reason. Then the car (its an 91 240 btw) sounded as if it has an open header. And at idle, the engine is rocking back and forth but above 2k its smooth.

I checked out the plugs, wires, and distributer but everything seemed fine. Although, plugs 2,3, and 4 seem a little hot (tip was a bit orange and the inside was very white). My guess is plugged injectors maybe?

I unplugged 1 cylinder at a time and it seems to act the same under idle when I unplugged all 4.

What do you think could be the problem?