I'm stumped! My 93 400E usually runs great, although I do not drive it daily. This problem started a month or so ago. I started the car for the first time in a couple of weeks and it has plenty of power and runs smooth until I drive it 5 or 6 miles. Then it loses power and runs very rough (almost like it was fuel starved). Sometimes if I mash it, it will straighten out and "surge ahead" but then does the same thing at the next stop light. The dealer said there is a lot of bad gas lately and they have seen this problem often. I then drove it 45 miles out of the area and filled it with Chevron Supreme and it ran perfect. I then parked it in my garage for about ten days and took it out for a drive today, and the same problem is back. One thing I did notice: When I got it home and shut it down today, there was a little wisp of gray smoke drifting out of the exhaust for several minutes after. Never saw it do that before and it does not smoke at all when running. This car has 88,000 miles on it. It only does this when I take a potential buyer for a drive. I usually do my own work, although I have always had BMW's. This little beastie is a different animal. HELP!!

Garry