Have the diagnostic fault code(s) read first, otherwise anything else is a guess. For running rough, only a few cylinders aren't firing due to spark, fuel, or compression problems. The additive you used is basically alcohol which absorbs moisture in the fuel. Most gas today already contains 10 percent alcohol so adding more is not necessary. It's not likely a compression problem occurred suddenly. I'm not qualified to think like a chemist, but if the alcohol you added and the alcohol already in the fuel are not compatible, I could imagine that the combination is harder to fire in the cylinders and requires a higher spark plug voltage. Your ignition system might not be able to reach that voltage which would result in random misfires. Perhaps the combination makes the fuel resistant to spraying from the injectors. If either of those are the problem, I suspect the rough running will clear up once the additive is run out of the tank. The best way to do that is to run it close to empty before adding fuel. If you just run it half empty, then fill the tank, you will be constantly diluting the additive but not eliminating it. Another thought is the additive burns hotter and damaged some of the spark plug electrodes. That won't clear up until the spark plugs are replaced. We used to worry about the cleaning effect alcohol had on the fuel system and where the dislodged debris would collect. There are screens in each injector that could become plugged but the filter really should collect that stuff first. I find it hard to believe that is the problem because one bottle of additive is about as much alcohol as you'll find in half a gallon of gas.
Sunday, March 20th, 2011 AT 9:02 PM