This soundslike an injector is staying open all the time and not shutting,you need to take them out and clean them in some solvent,or fit a new set.you can get them from sherlocks or motor works or motorbins,these are all good bmw spares suppliers in the uk.its common for an injector to become clogged with emulisfied petrol when it has been stood for a while.
adam bike doctor, March 2010