I had the same problem 3 weeks ago ! My car ( 2001 x5 4.4) was very responsive and powerful when it s cold . But after 15 min ( when it becomes warm) it becomes sluggish unresponsive ( like i was loosing torque) so i did a simple tune up : spark plugs, air and fuel filter , f
Cleaning the fuel pump and the injector ,( i changed also the overflow coolant tank because it was leaking) . My x is now a lot more powerful responsive when warm. ( forgot to say that i didnt get any code)