SMG engages clutch when decelerating at high speeds, rpm drops until engine dies

[sebastian bmw]

Hey guys I've recently encountered this issue. Yesterday while driving on the highway my car suddenly began to drop RPMs as if the clutch would engage every time I would ease off the throttle... Trying to understand what was going on, I was messing with my throttle while driving, repeated easing off the throttle, changing gears and it would occur on any gear... if I gave it throttle again the gear would be re-engaged and I could accelerate again... I let the RPMs drop all the way, expecting it to remain and idle and the car just turned off... turned it back on and the car had the same issue all the way until I got home...

While driving today, the car drove just fine but did drop RMPs once and turned off on me when I eased off the throttle on the highway. I didn't even notice it happen as I was just slowing down a bit. This only happened once today and the car drove fine after, getting me through the day with no issues. I've researched online trying to find someone with the same issues and haven't been able to find a reason for this to happen. Any help would be great!

I got a tire puncture the morning before this happened, tire pressure light has been on ever since as I am driving with a spare wheel while I wait for a new tire to ship in. I doubt this would relate to my problem.. what do you think?

Thanks!

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BTW I have an 04 M3 SMG with 103k miles

[GeorgeF31]

The clutch should always be engaged unless you are in neutral, stopped, or between shifts. If you can be in any gear and have the engine drop RPM until it dies/stalls, the clutch is probably not engaged when the engine does -- you'd also feel the standard clutch-stall lurch. You may have an issue with the SMG, but if taking your foot off the accelerator causes the engine to drop down until it dies, that's a whole extra problem. The SMG may be acting strangely because of whatever is causing that issue with your engine.

If you just brake without downshifting, does the transmission automatically downshift? When the stall occurs, do you get a lurch from the car in first gear or does the engine just die?

[jibbajabba]

Bringing this thread back from the dead.

Same issue. '03 M3 w/ SMG - Decelerate and the clutch slave engages dropping rpm to idle until you just touch the throttle and it whips back up to where it should be. Also, will randomly engage clutch slave and rpms rise until you release the accelerator. All gear sensors don't show it going into N, no fault codes at all, clutch and flywheel are good, new clutch slave, new gear position switch, swapped SMG brain...

Anyone come across this one before?

[MauiM3Mania]

Thread copied to the General BMW Mechanical Help sub-forum for assistance.

[bmwdirtracer]

Bringing this thread back from the dead.

Same issue. Decelerate and the clutch engages dropping rpm to idle until you just touch the throttle and it whips back up to where it should be. Also, will randomly engage clutch and rpms rise until you release the accelerator. All gear sensors don't show it going into N, no fault codes at all, clutch and flywheel are good, new clutch slave, new gear position switch, swapped SMG brain.

Anyone come across this one before?

Well, the very first rule of asking for automotive advice is to IDENTIFY THE CAR!

And second, well, George said it eight years ago: the clutch SHOULD be engaged at all times, when you are not in neutral, so you have a different problem than you think. If the clutch is engaged, it will keep the engine at the appropriate RPM for the gear it's in, not "drop the rpm to idle". That would be a DISENGAGED clutch. Suggest you go to a BMW specialist shop with a BMW technician and a BMW specific computer to diagnose the issue.

[jibbajabba]

Chris,

Sorry, I can see how that was confusing...the clutch slave is being engaged resulting in the clutch being disengaged. Which it should def. not be.

'03 M3 w/ SMG

[bmwdirtracer]

I would suggest that perhaps the hydraulic unit is what's failing, or the gearbox needs to be re-trained its shift positions.

I highly recommend taking the car to a BMW specialist that has ISTA (BMW's own diag system); the car will likely have codes which will lead ISTA straight to the shift relearn procedure, or a test plan for your issue. Oh, the hydraulic unit is no longer available.

[jibbajabba]

Hyd. unit is known good, gearbox adapted, clutch valve values and characteristic curves taught. ISTA, kicks back 0 faults. Clutch valve current, status and position increments does NOT change when it occurs (this makes no sense). You can see trans input speed drop, but shift travel doesn't change. Replaced EGS and updated, DME updated. Opus tech support never heard of it, brainstorming with other shop owners I know and nothing. Resorted to a little internet research, the OP is the only other occurrence I've come across...hence asking the collective brain hive of BF if anyone else has. Sounds like you never came across it either. It's a peculiar one, I'll update what it was for future reference.

[bmwdirtracer]

Thanks for being very specific, and for clarifying that you've followed through the normal faults.

Therefore, I have to now suggest that you either have a wiring harness issue,whereby the DME isn't correctly triggering the SMG / EGS module, or the DME coding is wrong, and it thinks it's attached to a normal manual trans. Maybe Abel will weigh in on the possible coding error. I have seen such coding errors (even in the EWS!! cause issues with dragging revs, etc., so maybe, just maybe ....)

I think if it were mine, I'd pull every plug on the DME, SMG/EGS module, and the trans itself, and clean them using WURTH ELECTRICAL CONTACT CLEANER OIL, (AKA "Magic Spray"). As you do this, make sure none of the pins are pushing back, or corroded, and there's no fluid seeping into the connectors through a sensor or plug.

Please let us know how you get on.