A flickering check engine light and rough idle on your F90 M5 usually means misfires. Start with ignition coils and plugs, but don’t ignore vacuum leaks or fuel issues.
Why is the light flickering and the idle rough?
When your M5’s check engine light flickers instead of staying steady, that’s your engine control unit telling you it’s seeing misfires severe enough to damage the catalytic converters. The rough idle is almost always the same story – cylinders are not firing cleanly at low RPM. On the S63 engine in the F90, this is commonly caused by worn ignition coils, fouled spark plugs, or a combination of both. But before you start throwing parts at it, there are a few other usual suspects worth checking.
