Today while I was driving to work after about 5 miles I merged onto a highway, at about 5000 rpm my car started running rough and the SES light immediately came on. I dropped down to 60 mph and approximately 2700 rpm, where it ran rough. After a few miles the SES light went off and the car ran smoother but wouldn't go over 3000 rpm. I took it home and parked it. Tonight I started it and the SES light didn't come back on. I ran a diagnostic tool and no fault codes were indicated. I didn't drive it to see if it was still in limp home mode. It has a 6 speed and 85,000 miles. I set the valves and replaced all filters, fluids and spark plugs 3000 miles ago and haven't had a problem from then until now. Would a bad coil cause this problem without triggering a fault code?
Sounds like your getting the half power light which will come and go with the issue. The problem with this is the fault codes will be stored in something BMW's calls shadow faults. Meaning a standard obd2 scanner can not see them unless they are happening currently. Possible a coil caused this but hard to say without having the faults.
Thanks. I'm leaning towards a bad coil as well given the mileage of the car and the fact that it ran rough until limp home mode.
