Engine Performance problem
2000 Renault Megane 4 cyl Two Wheel Drive Manual 68000 miles

i have the 2.0 megane monaco ide and my problem is when i get to about 4500-5000 rpm the car seems to pull back on power odd time orang light come on when driving car normally the car runs great all seems ok.i had a diagnostic check and showed 4 faults 2 unknown, one fault showed the lambda senser inavtive after the cat and the other fault was a fuel pressure fault any ideas on this as to which part i need or if its something else