[mipearson]

I'm a bit stuck. Bought a 2008 X3 3.0si with 110,000km (~70k miles).

Drives fine during the test drive. I do all the usual things - hard accel, soft accel, soft braking, hard braking, full left/right lock, etc. Seller arranges for it to have a couple of things fixed up (coolant leak, transfer case fluid) as part of roadworthy.

I pick it up a week later and five minutes later it starts to "bunny-hop" as if it's a manual with a learner driver as I'm getting up to speed. At this point I begin to suspect that I've bought a lemon.

(also for those comparing prices - labour & parts are much more expensive in Australia, in general)

Long story short:
(a) automatic transmission specialist shop close to me believes it is *probably* but (not 100%) the torque converter, will cost minimum $2k to pull the transmission out & send the converter off for a recondition. If that doesn't work - a new transmission would be ~$6-7k (inc labour). However, he mentioned that the transmission fluid didn't look as bad as it would normally for a cooked converter (or transmission), and that torque converter failures on these are relatively rare.
(b) my usual BMW mechanic (recommended to me by the 1 series forums here) took it for a drive with me and is completely stumped - would need more time with it, but he's a good distance away
(c) after confronting the seller (as having a car drive differently after you buy it is a bit suss), he got on the phone to the mechanic and got them to agree to cut-rate labour to fix up the problem. They want $2k for a second hand transmission, then probably a bit more for the labour, but it's all a bit suss as they were diagnosing this with me over the phone, and I have worry that they screwed something up when replacing the transfer case fluid which is causing all of this.

Other symptoms:
* problem gets worse under heavy driving - and I live in the hills, so all driving is heavy
* also has trouble working out which gear it should be in: think clutch slip like symptoms when accelerating from the lights, and it staying in an innapropriately low gear occasionally. Car has been driven at least 400km since the fluid change & the computer was told to reset.
* occasional whirring or grinding sound from under the seat, where you'd expect the drivetrain (but not the transmission) to be
* when the problem gets *really* bad, the 4x4 traction light flashes on as if it's losing traction

Tires are fine, same tread on all wheels. No idea what to do next as I feel like this doesn't fit under the usual set of problems when a torque converter fails.

Edit: have also disconnected the transfer case, as recommended elsewhere. No change.

[WrenchWizzardInTraining]

do a quick check for 2 things. first for your 4x4 type symptoms and the noise under the seat: transfer case actuator - there is a plastic gear that goes out over time. Simple/cheap/easy fix. here's a link:

second for your transmission symptoms: mechatronics sleeve/seal. basically, the plastic components attached to your tranny are worn and not sealing properly. here's a link:

[argejoegar]

Hi,

Did you ever find a fix for your problem. My daughter has the exact same vehicle and it started doing the same things you posted. Please let me know if you ever found what was the problem and if you found a fix for it..thanks

[mipearson]

argejoegar: I have not. I'm still trying to work out what the problem is in a way that doesn't involve spending thousands replacing things that might not need repalcing.

Did you have any luck?

[Eric206]

Hey there I’m having the same issue did anyone figure out what’s the issue ? No check engine lights, car feeling like it’s about to stall 4x4 light flashing

[ch1pch4p]

Unplug the transfer case actuator (you can do it from the actuator itself or the module in the back) and yes you'll have all your fun lights come on the dash, but see if it still happens. If it stops happening, it's something around your VTG. otherwise, I have no idea for right now.