Hi,



I’m experiencing an issue with an unstable idle, but the engine runs fine when applying throttle.



The car is a 2007 Mini One R56 with the N12B14 engine.



I checked the live data from the MAP sensor and got the following readings:

• approx 100 kPa (atmospheric pressure) with the engine off.
• approx 98 kPa at idle.
• approx 99-100 kPa when applying throttle.

Shouldn’t the vacuum be lower at idle as the engine builds vacuum?



Does anyone know what the expected readings should be?



Thanks!

 

I suspect the car is very close to sea-level elevation with those numbers. Remember, valvetroinc engines don't produce engine vacuum like a conventional engine.

I would look at you mass air flow numbers, fuel trims, and 02 sensor data.

Start by pulling up stft & ltft numbers at idle, 1500 rpm, & 3000 rpm. Post numbers. I'd bet you'll see a very high total fuel trim number at idle.

 

Hi,

I have posted a video here of short- and long time fuel trim.


Does this say anything to you?

Best regards

 

It would have been better if you performed the test without being in graph mode. I just needed the numbers at each throttle setting.

From the graphs you posted, fuel trims look good.

Next, we need to see if the upstream O2 sensor is switching. My sister-in-law's MINI (N12 engine) had the exact same issue. The DME was not setting an upstream O2 sensor code, but the sensor was slow to switch. Once I changed the O2 sensor, the rough idle problem disappeared.

Remember, O2 sensors need to be hot to function.

With your Foxwell scan tool set up just like you had it for the video you posted, and with the engine at operating temp, get a can of propane. Introduce some propane into the intake duct on the left side (driver's perspective) of the front grill. You should see the STFT immediately go negative, and I mean immediately. Meaning: the propane serves as a fuel source, so the DME will cut back on fuel (STFT) to maintain a stochiometric Air/Fuel ratio. The DME knows the mixture is rich based on the upstream O2 sensor, and will cut back on fuel flow (negative STFT). Once you cut the propane off, the mixture will go lean, and the STFT will go positive until the engine stabilizes. If you don't see these changes, you can confirm the upstream O2 sensor is bad by performing the same propane test, but while monitoring the upstream O2 sensor current (not voltage because it's a wideband O2 sensor). When you add the propane while monitoring the upstream O2 sensor current, you will see the current drop; conversely, the current will rise when you cut off the propane.