03 MCS JCW 100k miles

Runs great except for a bouncy idle. If I come to a stop with the clutch in, the revs drop down to about 500, bounce up to 1,000 and it repeats several times before the idle evens out.
There are no DTCs and the fuel trim is spot on. Any ideas?

 

It's a common thing with Minis, mine have a silly idle as well. I believe that most of the time this get fixed after a tune. At least I remember reading this on here, don't know for sure if it's a true permanent solution.

 

Strangely, this only happened recently. I've had the car for 10 years and it's never done it before.

 

Not my personal experience but have heard where a failing crank pulley can create this anomaly with idle, but as a whole bouncy idle is somewhat of a common occurrence with the R53's but not a chronic one ( every day ).

Some have also attributed it to a sticky valve, most feel it's the DME having a hic-up of sorts with programing.

My own 03' MCS JCW has 188K miles and has done the "bouncy idle thing" 3-4 times. Each time I would have to say it was after some "spirited driving" just before pulling into the drive.

 

Interesting. I installed an ATI super damper last year and have done less than 5K miles in that time. I don't think that's the issue.
I did in fact notice this anomaly while tearing up some twisty roads. "Spirited" is a serious understatement. The Hawk HP+ pads were fading.

I was beginning to suspect a vacuum leak. This wouldn't necessarily throw off my fuel trim, but would certainly screw with the idle adaptation values. I might scan the DME again and see where those numbers are.

I just find it strange that after 10 yrs, this is the very first occurrence of what everyone claims to be "normal" behavior.

 

You might want to go through all of the vacuum lines coming from the motor and make sure you don't have a leak.

 

My guess would be some form of air leak. Maybe even check your intake but I think that would be noticed when you rev it would come down slowly or hang up and idle high for an extra second.