Finally, the problem was solved! It was the throttle housing assy failure. Dealer replaced it and everything backs to normal now. Since I replaced this part on 3rd May 2006 due to the same problem, this time dealer replaced the throttle under warranty (in HK, BMW dealer provides two year warranty for any part replaced by them), I just paid about US$100 for inspection.

One more thing, the dealer tried to fool me around by not mentioning this part was still under warranty and they tried to replace the MAF meter as well for me and charged me more than US$1,000 for the two parts including labor. They told me that they found fault codes of both throttle and MAF meter in DME, but I believed that only the throttle was failed, not MAF meter (I have experience on this proble before). Fortunately, I keep the repair invoice to show them that the throttle was replaced by them within 2 years and claimed warranty, also I refused to replace the MAF meter and ask them to re-install my old one back on, my x runs fine without any problem now. But I will buy a new MAF meter from outside dealer for only US$180 (bosch product) and replace it myself. Dealer charges more than US$640 for the part.

By the way, can anyone here tell me what will happen if the MAF meter starts to fail? Thanks!

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--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.