Engine Performance problem
2001 BMW M5 V8 Two Wheel Drive 108000 miles

Gentlemen I have a 740il 2001 BMW I have a code scout 1500 code reader, when my service engine light comes on the car tends to run very poorly from a dead stop, after a couple of days the engine light goes out and the car runs fine, the code reader gave me a fault code of P1158, can you give me a clue where to start trouble shooting, dealers are telling me it has something to do with the Transmission, shops are telling me its the air mass sensor. Help

I'm confused, is this a 740il or an M5 ? Also, what has been done so far? Has the DME been reprogrammed or the precat 02 sensors replaced yet? Adaptations cleared? Any other faults?