I´m having running issues with my X1. Engine is ´kangarooing´ ie losing a cylinder and back firing through the throttle body. I´ve checked spark and replaced spark plugs, still the same. When I again checked plugs they were both black and grimy, which suggests a fuel issue? Next I checked the injectors for blockages/reside, they both fine. So now I´m thinking the fuel pump or fuel regulator. Any ideas or opinions would be appriciated. Best, Matty