My source is the dealer and its the V8's.. It is a serious engine defect which is caused by the DME. Not sure of the details but the only resolve is replacing the engine which costs BMW Canda around $26,000 on an X5 4.8is. Dealerships were having to drive loaner cars up to Muskoka and towing back people's 4.8's to do replace the engine. Unbelieveable!