Sulfur odor is poor fuel quality or cheap gas. Sometimes diagnosed as catalytic converter issue. Purchase some high octane +93 octane for a few tanks, from a respected, well visited fuel station...Shell is what i use - 93 octane. Try that and see what happens. Otherwise it is the fuel mapping on ECU.
X50 w/ M-Perf. 15.6 MPG on almost 9K miles. City and Spirited Driving. Top Speed 133mph...so far.