Exhaust Sputtering

[nicktheknife]

Wondering if someone could help me out. When my engine is runing, I hear a sort of popping/hissing noise from the drivers side of the engine, more noticable at idle. Also when I let off the gas in gear the exhaust sputters, but it pulls strong on acceleration with no sputter at all, and I have noticed a little bit of white smoke coming from the exhaust intermittenly at idle. I have just replaced the distributor cap and rotor, plugs and wires, pcv valve, and thermostat from 195 to 180, and it didn't make this sound before that or blow white smoke, or maybe I just didn't notice. Any suggestions?