ngk iridiums

[brs86supra]

i was wondering if anyone has had any problems with the ngk iridiums xi. and what there supposed to be gapped at. the plugs are all black and they are new plugs. and if they are gapped wrong could it make your car idle rough. like for example when im in idle, the exhaust breaks up and black specs get over everything behind the car, and when i give it some gas in neutral it feels like it wants to shut off. or could these problems be due to my timing not set right, like to high (higher than 10 degrees) any help woould be greatly appreciated