if the smoke it black then one or more of your cylinders arent firing so it could be anything related to your ignition (plugs, coil packs, injectors).. from what you've said it could be your coil packs.. in the meantime take your coil packs off and lightly sand the inside of them.. this part:
make sure it looks something like this when you're done:
its worth a try and it wont take much of your time.
i did this to my car when i had a misfire problem and it fixed it right up.