Knock sensor

I have a 1997 transport / montana 3400. we have finally got the driveability problem narrowed down to a timing problem. If you unplug the knock sensor the engine runs near perfect. Plug it back up and the engine wants to buck jump,no power, and the temp goes up a little. replaced knock sensor. no change, same symptoms. the engine still run's a little funny,(kind of like flutter). but it's where most people wouldn't notice it. any ideas.