What codes did you get? Limp mode for me was caused once from a loose alternator power nut, (fell off the connector got so hot it glowed) twice from transmission connector getting water in it and once had a long time issue with each of our cars with random cylinder misfires. Mine was plugs hers was a bad coil and dirty injectors.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)