Mini Cooper R56 Idle Issues and Engine Stalling

Hello everyone, I own a 2008 Mini Cooper R56 with the N12 naturally aspirated gasoline engine (120 hp, non-turbo) and a mileage of 150,000 km. Ever since I bought the car, I’ve been experiencing an issue with the idle that still hasn’t been resolved. When I first start the engine (cold start), the idle fluctuates significantly. The car starts shaking like it's about to stall. The idle drops too low, then it revs up by itself again. After the engine warms up, the problem continues in a different way — for example, while waiting at a red light, the idle suddenly drops to around 450–500 rpm and then climbs back up again. About 2,000 km ago, I had a full engine and transmission rebuild, but the problem existed before the rebuild and still persists afterward. Almost every sensor and component related to idle and air-fuel mixture has been either replaced or tested. Still, the problem hasn’t gone away. It’s becoming so frustrating that I’m genuinely starting to lose all enthusiasm for the car. Has anyone experienced something similar? What could be the possible cause? I’d appreciate any help or suggestions. I'm honestly exhausted from chasing this issue.

17 comment(s)

Quotation:
@cemocn wrote on
MAF sensor, oxygen sensors, camshaft position sensors, vanos solenoid valves were all replaced. Almost many sensors were renewed.

Check the engine's ground connections and battery terminals for corrosion or looseness, as poor electrical connections can lead to erratic idle behavior. Ensure all connections are clean and secure. Let me know if this resolves the issue or if you have further questions.

Quotation:
@CarlyMechanic wrote on
Inspect the mass airflow sensor (MAF) for any dirt or malfunction, as it plays a crucial role in managing the air-fuel mixture. Cleaning the MAF sensor with a dedicated cleaner might improve the idle stability. Please let me know if this helps or if you have any further questions.

Any idea?

Quotation:
@cemocn wrote on
Any idea?

Consider having the ECU (Engine Control Unit) checked for any software updates or potential faults. Sometimes, a reflash or update can resolve persistent idle issues. If the problem persists, consulting a professional mechanic with experience in Mini Coopers might be beneficial. Let me know if you have any further questions.

Quotation:
@CarlyMechanic wrote on
Inspect the mass airflow sensor (MAF) for any dirt or malfunction, as it plays a crucial role in managing the air-fuel mixture. Cleaning the MAF sensor with a dedicated cleaner might improve the idle stability. Please let me know if this helps or if you have any further questions.

Any idea?

Quotation:
@cemocn wrote on
Any idea?

Check the fuel injectors for any clogs or malfunctions, as they can affect the idle if not operating correctly. Cleaning or testing the injectors might help. Please update me on your findings or if you have any further questions.

Quotation:
@CarlyMechanic wrote on
Check the fuel injectors for any clogs or malfunctions, as they can affect the idle if not operating correctly. Cleaning or testing the injectors might help. Please update me on your findings or if you have any further questions.

All four injectors have been changed. Engine ECU has been updated and battery connections are intact. Problem persists :(

Quotation:
@cemocn wrote on
All four injectors have been changed. Engine ECU has been updated and battery connections are intact. Problem persists :(

Inspect the timing chain and its tensioner for wear or improper tension, as these can cause idle fluctuations. If the timing is off, it can affect engine performance. Given the complexity, it might be best to have a professional mechanic evaluate this. Let me know if you have any further questions.

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