Yesterday, When I was driving my X, suddenly the engine lost control. When I stopped it at red light, the engine run like someone pressed the gas paddle and released it and again and again, after I released brake, the car just speeded up and slowed down followed with the weird engine behavior, but I did not press the gas paddle at all.. The RPM of the engine just run to 2000 and backed to normal and then did it again and again after I changed shift gear from 'D' to 'N'. I pull it over and shut down the engine for 10 minutes, then start it again, the engine just did it again. No light up, no warning in the cluster, the engine did not die itself. What is the problem?

One year ago, I encountered the same problem, but difference is the engine died after several self-speed-up and self-speed-down and come with warning of 'engine failsafe prog' in the cluster. I had my car checked by dealer, and found that it was the throttle assy failure. But this time no warning, no light up, no engine dead, only self-speed-up and self-speed-down.

Any input is very much appreciated!!!

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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.