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Hey all, Hopefully by this post I can narrow some searching down. I have found some similar issues in the posts but nothing quite like my so far. I have a 2009 Mini Cooper S with the JCW conversion. I bought the car in parts due to the classic timing chain guide exploding. I have it all back together and running great now! Although it was missing the Ambient air temp sensor (reading -40 in the cab). So I ordered a new one and installed it. After installing it, I went to run some errands only to have the car go into limp mode after the first boost build. I pulled over, turned the car off, restarted and took off again and felt the boost kick in just fine but went immediately into limp mode again. Once I got home I unplugged the Ambient air temp sensor and it builds boost just fine no problems driving around town. It does not throw any codes when I hook up the code reader either.
MAP sensors are different between JCW and MCS --- different boost levels allowed. Maybe the IC pipe unit has a different temp sensor (for air intake temp) too, and doesn't like working with an MCS ambient temp sensor. I suggest you ensure both MAP and ambient temp sensors are all the correct versions --- https://www.realoem.com/bmw/enUS/select for part numbers.
Hard to believe there's no codes with a limp mode. You should invest in a good Mini code reader.
I'm clueless about what makes up the JCW conversion kit, so I'm suggesting you ensure part numbers are correct. Not all owners are aware of the sensor differences, and a previous owner may have installed the wrong one.
The 09 JCW tuning kit is still an S, so it should still use all the S sensors. It’s possible you will need to replace some sensors, since the car is approaching 12-13 years old.
My suggestion would be to invest in a proper code diagnostic tool, and learn as much as you can on these cars. Get familiar with realoem.com which is a good reference for part numbers and parts schematics. Using google to search these forums can be helpful when looking up any issues.
