The S5 ecu's will go into limp mode for many reasons. It could be a bad oil metering pump. It could be the TPS out of adjustment. It could be other things even as simple as something small not plugged in all the way. In limp home mode, the car runs like crap. It makes no power, won't rev easily and definitely not very high. It is just plain hard to drive altogether but still possible. If you have been driving the car 23+ miles a day for a while then I would suspect that it isn't limp mode but rather something else. You would have stopped driving it after only 1 day if it were in this mode. Then again I haven't seen your car so I can't tell. If the oil metering pump went out a couple of months ago then you probably wouldn't have an engine now. No lubrication to the engine would be very apparent very quickly. The OMP's did have some issues on those cars from time to time but if yours has been replaced and the car runs the same, then that wasn't your problem.

It's a little late now but I have an S5 OMP lying around that I don't need and I know it works.

 

sounds very familiar, bogs badly if you try too much throttle,sputters or bogs in any gear if you accel too hard, also check engine light on,code 27 or code 20

 

noted other replies,i drove mine for approx 30 days,60 miles per day,noted that lines did have oil in them,dealer
misdiagnosed,due to faulty test equipment,only when we counted flashes did we find correct code,