Hi Neil and

from Mid-Wales.
My Z4 had a problem with fluctuating revs as the brake pedal was used, when I first bought it. It turned out to be a split in the rubber hose from the MAF, got that sorted and he now runs like a dream. I got 43.6 MPG out of him on the run down to Brighton from Mid-Wales.
Hope your problem will be as easy to sort out

.
Colin.