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.

 

Following.
I occasionally get a low idle when approaching a stop, or idling in reverse [in motion].
Keep meaning to start a thread on it, but forget.
Mine doesn't have the cold start fluctuation like the OP, just on decel right before stopping as it drops to idle & at idle in reverse.

 

Identical car and problem here. Tried changing identical sensors.

Cemocn - does yours also drop revs when fans come on? Have you tried driving with MAP connector unplugged? I know it is no solution, but at least fixed the erratic revs for me temporarily while I'm trying to figure it out.
Starting to suspect the alternator.

 

Sounds like an intake air leak, for example PCV or Evap purge valve. Any fault codes? Do you have a scan tool?

 

Mine was in 3 shops, all of them reported no fault codes stored (except for the led bulbs, but unrelated) also from what I can see ond the dash in the menus, no faults (except again the occasional bulb warning because of the led-s).
New PCV valve installed. New hose running to the intake manifold. Sprayed brake clean and MAF cleaner around intake manifold - no changes in rpm.
Any other way I can check the evap purge valve?

 

Pinch clamp hose at valve and/or disconnect hose at IM and cap IM nipple -> Check whether idle smooths out.

Looking at live data with a scan tool could be very useful.

 

Thank you for the advice Maybe. Probably will have to wait for saturday to try it out, as it needs to happen early morning before I drive off to work. Only then is the engine cold enough for the chasing/droping rpms to happen. And tonight we have a storm incoming. Definitely posting results as soon as I get to it.

 

You can also test for any vacuum/air leaks using water or starting fluid, spray around every pipe and coupler and see if the RPMS drop (with water) or increase (with starting fluid). Do one piece/area at a time so you can pin it down if this is the case. Make sure to hit the tiny vacuum lines under the intake manifold as well. It could be a very small crack in the hard plastic lines if not the intake/intercooler piping.

 

So, it has been a couple of days since I tried unplugging the evap valve. The results are mixed ..variable revs did not change, still doing the same thing when firing up cold and coming to a stop. However the terrible knocking sound I had did stop.

The new issue seems more complicated, the car is not reporting any codes whatever sensor I unplug, nothing lights up ..I have since visited a BMW specialist, and was told the engine fault module might have been deleted with a remap. The reprogramming is going to be between 200-1500eur, depending on whether the ECU survives and what has been done previously to it. On top of that, it was most likely done to cover up the defective valvetronic and vanos system, wich will most likely be another 2-3000eur.

 

:(