Hi, My 1995 EG d15b7 Honda civic (not modified in any way) has a flat spot between 2000rpm and 4000rpm. I have tried new plugs, new fuel and air filters, checked timing, new plugs, different plug gap, fuel cleaners and better petrol, checked resistance on leads and cleaned the distributor cap and button but the problem does not go away. Does anyone have any ideas on what it might be or how to diagnose it. Regards, Mike