|
If the plugs have more than 40K miles then they should be changed and not waste money on diagnostics. The transient misfires that will not allow DME to detect the misfiring will not go on too long before it worsens and the misfire is detected and warning light and messages appear. Transfer clutch stick/slip can go on for a long time and never get sensibly worse or give warning message and warning light. Ignition coils that fail when plug gap is too wide from too long use will sometimes "heal" for a time with new plugs and then the misfire comes back again with a code for the cylinder in most cases. The coil failure issue is why you see plugs and coils recommended to be changed together. On many makes, not only BMWs.
|