I am running a E30 1990 318i and for over 2 years I have had this very intermitant problem. About a year ago it got quite bad and went into the shop whereupon in miraculously failed to misbehave - typical!

The symptoms are most obvious when drive at freeway speeds and takes the form of a reluctance to pick-up power at the bottom of a hill. At that point it will carry on at about 60mph but starts missing if you give it too much gas. After about 5 minutes it gets 'better' and returns to normal. Possibly or possibly not associated is a strong smell of gas inside when the car is restarted.

Otherwise the car is so reliable and I would like this to be the reason to part with it!

Hope someones has some ideas?

Have you looked at getting a general tune-up?