2000 Boxster Smoking issue

[Rreecer13]

I've got a 2000 Boxster S that recently started to have a rough idle and fuel mileage dropped off some, not much but about 10-15 miles less per tank. I puT a bottle of Berrymans B12 Chemtool in a full tank of fuel to see if that would help clear up the rough idle. I thought maybe a fuel injector was dirty. The rough idle cleared up after just a few miles of driving. Thought the problem was fixed. The next morning when I went out o go to the gym, I started the car and huge clouds of white smoke came out of the exhaust. Smoke went away after the car warmed up. I spent about two hours at the gym started the car, again big clouds of white smoke. Got on the interstate to go home. Accelerated again huge clouds of smoke. Not continuous just during acceleration. Check engine light came on, flashed about 5 times the went steady. It's till on. Took the car to O'Reillys to have the code read but their machine wouldn't recognize the car. We don't have a Porschedealer here. Any ideas?? I had one mechanic tEll me to run that tank of gas out of the car and fill with fresh 93 octane.