Do you have a code reader? A friend with one? Or can you stop by an auto parts store that will read the codes for you? When you have the codes, post here and we'll diagnose. Could be as simple as a worn out O2 sensor...
2008 535i - Monaco Blue/Tan Leather, Sport, Premium, Cold (+ heated rear seats), Navi, HUD, PDC, CA, Sunshades, Fold down rear seats, CPO, Extended Maintenance