I have a 2007 IS 250 AWD. Last year I had acceleration problems. I took it to the dealership 5 or 6 times as well. They could never recreate the problem. Ultimately they figured it out. If my memory serves me correctly, it had something to do with an engine cylinder problem. My dealership is Tom Wood Lexus in Indianapolis. My Service Tech's name is Shanan Jackson.
John T.