Once my R56/Auto w/ 60K, warms up it doesn't like to idle. It 'bounces', goes from ~700rpm to ~1200 rpm and gets worse and worse (~400-~2000). Sometimes so bad it will stall. Sometimes it (best way to say it) burps, then all is good. Then it gives me codes about 15-20 seconds later.
Happens in drive (or reverse) mostly, but also in neutral or park. Makes me think it's not tranny related, because sometimes once it starts bouncing up and down and it's not too bad, (yet), I can slide it into neutral, it will settle down, sometimes it won't and will continue to bounce while in neutral. It's a crap shoot.

Codes: 2786-present,Additional Mixture Adaptation & 2B64-not present,Intake unmetered air. Sometimes, I even get (all) the misfire codes, but thats seldom and only when it gets really bad.

So If you read my thread on my turbo not working then you know I've taken it to 2 mechanics about the turbo issue (it's my only other thread). This started when I left the first mech before I went to the second. The second mechanic was very thorough with my first issue so I can't think of what this could be...

Being a very good shade tree mechanic it sounds like a vacuum leak (unmetered air), but this car has been smoke tested twice, because of the other issue.
I've also vacuum tested the vac pump, vac lines, all hold vac. Don't really think it's true unmetered air, but MAF not agreeing with the O2 sensor while it's bouncing the idle.

Here's my list of new parts, some of these were replaced due to the turbo issue, some from a horrendous oil leak left by the former owner, the last from this issue:

ALTA CAI, downtube, intake tube, catch can (these were before any issue, done to clean up the engine bay, and they look cool..)
MAF
MAP
Boost/Temp sensor
Pressure Reg (vac solenoid for turbo)
Turbo vacuum lines
VANOS solenoid
Cam chain tensioner (also inspected cam chain, guides, etc, all look fine)
Changed ATF, checked level a couple times (I had a Dodge Dakota that would stall if the tranny fluid was low, if anything it's a touch high in the Mini)
...Changed after cycling/bouncing idle:
PVC/Valve cover
Second PVC tube (in back) removed and capped off
Both O2 sensors
gas cap

​​​​​​​I'm now thinking plugs and/or coils. But if one or two of those are bad wouldn't I just get misfires just for those, not all four misfires?
It also smells of sulfur after a hard drive, catalytic converter bad?

The car runs great, but just won't idle right.

 

It sounds like you have a vac leak to me. But you said its been smoke tested. so I don't know, but It looks like you have dug into the car quite a bit between yourself and the 2 mechanics you have been to. Just from experience before throwing any more parts and $ at it, check everything, then check again. it is most likely related to the work that was recently done.... either something is not connected properly... bad connection somewhere maybe..or not plugged all the way in? I know you have looked already, but do it again. I have checked 3-4 times before seeing something I've missed before.
good luck and keep us posted

 

I kinda thought that was going to be the plan. Maybe a loose intake manifold bolt, or the evap-can hose.
Something that doesn't leak all the time, like only when it warms up or when the evap-system turns is activated.

....back under the damn car. Good thing I like working on cars/jeeps/motorcycles.

 

I had the same symptoms on a 2009 Mini Cooper JCW with 106k miles on it. My problem ended up being the MAF sensor. I looked for actual vacuum leaks and found none, then noticed that the MAF reading was sometimes shooting up at idle. Disconnecting the MAF sensor smoothed out my idle which sold me on the broken MAF. I replaced it and haven't thrown these codes since.