The way you describe the running backwards and smoke I tend to believe you have an ignition based backfire in the intake. Since the ignition is computer controlled it will be hard to test in the field. The one exception to this would be the cap and rotor. Definitely not the easiest, and as a result it is not often inspected during servicing. Its also well built and expensive enough not to shotgun at every service as one might on a Domestic auto.
If it is in the cap you will probably see it on disassembly. The center terminal of the cap and the rotor resistor often blow out. The rotor can short to the shaft without visable evidence though. If you go in at least replace the rotor.
Bosch Master, ASE Master, L1
33 years MB technician