Hey, been searching a couple of Mini forums for similar issue to mine, with no success, so decided to create this post with hope some of you might have knowledge on what to do.

Currently I do have P0420 issue coming up all the time with not really rough, but definitly uneven idling.

Short chronological background:
1. Bought the car used in January this year, during the test drives and all inspections car seemed to be in very good mechanical condition, idling was perfect.
2. Have been driving it for around 1k KM with no issues, but I wanted to have complete car service done so it is not in v good, but rather perfect condition.
3. Changed everything in car the mechanic advised. Engine related stuff is mostly spark plugs, timing chain, water pump, thermostat and some turbo tube. Other than that got K&N ait filter and what I belvie is crucial engine remap.
4. On the way home, around 150km in I got the first Catalytic Converter codes P0420. Started noticing some uneven idling - this was getting worse to the point of:
5. After bried check to make sure it is nothing too crucial was driving with it for next 3 weeks, to the point when (not sure if related) I had blown one of the coils on the cylinder. Had it replaced in local shop. Still uneven idling, but not as bad as before.
6. Had exhaust done, but only replaced middle section to straight pipe and put on JCW muffler.
7. Came back to the full service place with the code, they had replaced the cat to a new one and let me go. On my way home, again around 150km in the P0420 pops back up.
8. Got to local shop where I had replaced the coil asking for diagnosis and they seeing how cat is perfectly clean pointed to the ECU remap.

What might be important is that:
a) First and third time I had the engine light come up after servicing was after strong, long pulls in second and third gears.
b) This might be dumb, but fuel economy seemed much better with the engine light on, than with it being straight after error clear. Maybe it is just that it is giving me less power with the light on, but it didn't feel any slower really.

So here I am reading how P0420 is caused by bad cat, bad O2 sensor, exhaust leaks or engine timing issues. Cat is out of the question, O2 sensor I do not know if it is replaced with the cat? Exhaust leaks seem out of the question as it was bad both with stock exhaust, after replacing middle and muffler and then later after changing cat. So that leads me to belive it is engine timing issues, which as far as I undestand can definitly be caused by poor engine mapping.

Please advise what could the issue be and correct any flaws in my though process and understanding of the situation. Thank you.

 

Maybe a bad wire going to the cat, check that and also when you install the oxygen sensor and use a socket that pushing down on that sensor wire i seen people damage the wire on a new Oxygen sensor.

So you have a new factory cat or replaced with used full downpipe?

 

Okay, thanks, I'll have that forwarded to the mechanics when I drop my car for next check.

I belive I do have a new factory cat.

 

Anyone know where to get the special socket to remove O2 sensor N18?

 

I like this one as it does not hurt the wire.

https://www.ecstuning.com/b-schley-p...sly88750b~sly/

 

now this is great!!!

 

Hello, did you find out what triggered the code?