This BMW came in with multiple cylinder misfires, we scanned the engine control computer and found errors for misfires and an error for a lean condition. Our BMW factory trained technician suspected an air leak in the intake system. He connected to intake system to our smoke machine to check for intake leaks. He found leaks at the main intake air boot and the oil cap. A modern German car can not have air leaks in the intake system or the crankcase, because the crankcase is a sealed to the intake system, an air leak at the oil cap will result in an air leak in the intake system and therefore a lean condition. In this case the primary leak that was causing both errors was from a badly damaged intake boot, but we replaced both defective parts. This leak was big enough we probably could have found it without the smoke machine, but the machine is invaluable for finding smaller intake leaks and evaporative emission system problems.