Hello, I have a 2008 Mini Cooper R56 with an N12 engine producing 120 horsepower. It's the non-turbo model. When I first start the car, the idle fluctuates. The car shakes as if it's choking, the idle drops, and then revs up on its own as if it's accelerating. Once the car warms up, the idle occasionally drops to around 450-500 RPM when stopping at red lights before stabilizing again.

The engine and transmission were fully overhauled 2,000 km ago. This issue existed before the overhaul and still persists afterward. Honestly, I’ve grown tired of the car because of this problem. A smoke test was performed, and there were no leaks. There are no fault codes registered in the ECU. The MAF sensor, PCV valve, VANOS solenoid valves, and gas cap have been replaced. The canister (fuel tank ventilation valve) was checked and is in good condition. Almost every part and sensor has been replaced. The ECU was also updated with the latest software, but the problem still continues.

Has anyone experienced a similar issue? What could be causing this problem? I’m genuinely frustrated and would appreciate any advice or suggestions.