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?