I tried to replace the timing chain tensioner on my N12 base Cooper last night to hopefully reduce/eliminate cold start valve noise and hit a snag. Everyone says it's "easy peasy", but there's no way to get a socket on the damn thing with the throttle housing in place and I'm not sure there's enough room to remove/reinstall the tensioner with the housing in place even if I were to go out and buy a 27mm wrench specifically for the task.

Consulting the Bentley (130-15), the job appears easy enough. 3 torx screws, one electrical connector, and I'd need a new gasket. However, Bentley states, somewhat forbodingly:

"After re-installing, use MINI scan tool to check for fault codes and reset ECM memory. Reset throttle plate adaption values following on-screen directions. If the adaptation process is not completed correctly, the engine does not start."

It doesn't state whether this is required when re-installing the same throttle housing, but I really don't need this job to end in a no-start and tow for me. Is the ECM reset part really required? I don't see any mention of the throttle housing in other timing chain tensioner replacement posts, but pretty much all of those deal with the N14 instead which has a completely different setup in that area of the motor.

 

None of the readers here have done this on an n12 base Cooper? Is there another way to accomplish the task that I'm not seeing? Bentley doesn't cover this job specifically, and as mentioned earlier, the guides out there are all for the n14.

 

Result for the archives:

This job is not possible with the throttle housing in place on the N12.

Disconnect negative terminal on battery
Remove air filter box and rubber elbow to the throttle housing
Remove throttle housing Torx screws (x3) and move housing aside, removal isn't really required

After that, tensioner replacement is super simple. Unscrew the old one and screw in the new one. You'll need a 27mm socket, I used the socket I bought for the oil filter cap. My old tensioner had very little spring pressure left to it.

Put throttle housing back in place with new gasket (less than $3 from Advance, they had to order it but got it in that afternoon)
Re-assemble air intake system

Re-connect battery
Start car, let it run for a minute, then shut it down and check the oil level. The tensioner doesn't hold a ton of oil but it does seem to hold a bit.

The hardest part of the whole thing for me was getting the new gasket into its slot on the intake manifold, and that wasn't really difficult, just fiddly.

 

I have done mine, and as this N12b16a video shows, just remove the screws and set throttle aside, no need to disconnect and also no need to reset ECU with OBD. I did not replace a gasket either and no problems.