My new-to-me JCW makes a jerk/jolt/hiccup while decelerating in gear. Not violent but easily noticeable and consistent. It always happens around 1400-1500 RPM and I can make it more pronounced by braking. It feels like the engine gets a quick throttle input or extra bit of fuel for a split second.

The car is currently in the shop for a new clutch due to a failing throwout bearing and bad flywheel. However, the shop’s current theory about the jerk is that it’s effectively “normal” and the result of the supercharger boost being released “like a waste gate.” I don’t think I’m buying that… The bypass valve was recently replaced and the jerk hasn’t changed, nor is there any yo-yo phenomenon. I recently also replaced the fuel filter, and plan to do the injectors soon.

What do you think? Does your R53 do this?

At this points my thoughts are either:

• Throttle body or injectors (however, no CEL and the usual codes)
• Aftermarket tune (as far as I know the car doesn't have a tune but maybe there is one)
• Shop is right that there isn't anything out of the ordinary

 

Following up on this, we've discovered numerous exhaust leaks, the worst being the flange for the exhaust manifold, in addition to the flex pipe and almost every weld downstream. Hopefully replacing all of that will smooth out my issue.

 

i had an odd pull come about after doing some suspension work. it would pull slightly on initial acceleration and when i first let off the gas.

turned out i had forgotten to tighten down a ball joint and the bolt was working itself loose. so...give the suspension and steering components a good once over, perhaps.

 

My '03 MCS which I've owned since new has a habit of "surging" when letting off the gas - it's intermittent and haven't been able to recreate it reliably. I've decided it's just another "quirk" of these engines - of which there's a few (random rough idle that goes away if I tap the gas, stalling immediately upon starting and then starting up again and running perfectly, radiator fan will not turn off if I turn off the A/C).
Interestingly, I've found that the surging hasn't occurred as frequently ever since I installed and Detroit BPV

 

I wouldn't use "jerk" but rather just a small "hiccup". Every mechanic I brought the car to for this problem called me crazy for even noticing it. I have had 3 minis so far and across all of them, they have that same hiccup/jerk around 1200 rpm. It doesn't really affect the driving of the vehicle so I wouldn't bother with it.

 

could be the stock tune. the tune has "burble". that means it continues to inject fuel after you come off throttle. just a guess