Hello,
Yes, plugs and coils can cause the powertrain control module to set the reduced power mode (limp mode or safe mode). The problem is, so can many other issues.
Now, BMW has their own set of propriety codes that you will need a scan tool to access. You don't have to spend 1000's of dollars, but you will need one that will read BMW manufacturer codes, not just standard OBD codes.
Now, there are also codes that will show up on the OBD-II side, and those can be read with any OBD-II code reader (model year 1996 and up).
If you have a misfire, you will show up with codes P0300, P0301, P0302, P0303, P0304, P0305, and/or P0306. It could be one or any combination of those. If you find this is true, the spark plugs and coils could be causing it, but they seldom all fail at once. Other causes of misfire would be vacuum leaks, failed turbochargers, boost leaks, faulty injectors, mechanical damage, and the list can go on and on.
Let me know if you need any more assistance, and scan for trouble codes before you buy anything else.
