I have an 2009 59 plate LCI E91 318i M Sport touring which shows all the classic symptoms - bought as a BMW AUC in July 2012 with 25k miles it went back after 1 week for misfiring and poor running and had all the coil packs and plugs replaced, then went in on recall to have the coil packs replaced again! Since then, it has been back for poor running, misfiring and intermittent power delivery twice.
My dealer has investigated the latter 2 events and the only fault code showing has identified the need for a de-nox which has been undertaken twice to no avail. They have run a journey memory check and have suggested that we need to do longer journeys as the usage indicated usage under 20 miles ordinarily! I have rejected the vehicle on the basis that it has had a pre-existing fault since delivery in July 2012. BMW UK has said it disagrees but has offered an extra 12months AUC warranty as a sweetener. I have acknowledged their offer but made it clear that the pre-existing fault is legally an issue between myself and the supplying dealer under the Sale and Supply of Goods Act 2003. Having held a 1:1 with the Dealership AUC Manager and Service Manager on Friday I await the next position - such fun!!!!