RPM's fluctuating at idle - then engine stall

[PhillyfaanM3]

I thought I would share this with everyone just in case you are experiencing something similar.

So, I drive a modified (I would describe it as conservatively modified) 2011 BMW 135i Convertible 6spd (N55 E88 with 25k miles), the list of mods are in my signature. I only drive about 4-5k miles a year.

Last year I experienced what I would describe as erratic/fluctuating RPM at stop/idle on two occasions. After driving the car with no issue and when at a complete stop, in neutral the RPM's would be resting at around 1k RPM but would then drop to 500 RPM's, jump back to 1000 RPM's and fluctuate between 1k to below 500 RPM's. On one occasion after fluctuating, the car just stalled.

This year after having the car out all season, I recently began to experience the fluctuating idle more often and again recently experienced the stall.

I went online and couldn't find anything definitive, I saw similar examples of other users describing this erratic idle and in most cases they were speculating that it could be everything from the MAF sensor maybe needing to be cleaned, to airfilter to bad gas.

I contacted my dealer and showed them a video I took of the RPM's fluctuating and he explained that BMW is starting to see more of these in both manual and DCT cars. He explained that BMW had released a TSB for this requiring an upgrade to the SW and for me to bring it in.

He also shared that the DCT cars would also need a SW upgrade for the Trans.

My plan is to take it in next week to see if the SW upgrade will resolve the issue.

Hope this was helpful.

[Esteban]

Hmm... interesting Frank. We normally hear about these kind of issues with the DCT 135s, although it's usually the RPMs climbing at idle, not dropping, so this sounds like something different. Hope the software update helps. Please keep us informed.

[ejm3]

I have a 2012 135i convertible (no mods) and this has happened to me a couple times, though not within the past year or so.

For me both times it happened when it was hot out, though the AC was not running either time.

There have also been a couple other occasions where I felt like it would stall but never actually did.

If I take it to the dealer for the SW update will they charge me for it?

[PhillyfaanM3]

Originally Posted by ejm3

I have a 2012 135i convertible (no mods) and this has happened to me a couple times, though not within the past year or so.

For me both times it happened when it was hot out, though the AC was not running either time.

There have also been a couple other occasions where I felt like it would stall but never actually did.

If I take it to the dealer for the SW update will they charge me for it?

ejm3,
Since BMW has rolled out a TSB for it, the dealer should not charge you for it. I would call your dealer and share your experience and share what I've posted. They should be able to see the TSB and schedule it for the SW update.

[Athseef]

Mine did the same, followed by a burp of white smoke out the exhaust a few minutes later. The dealership determined it was a carbon buildup issue and did a walnut blasting. That noticeably improved throttle response and engine smoothness, and it has not had a similar issue since.

[ejm3]

Thanks Frank, I'll talk to my dealership.

How many miles before the walnut blast becomes necessary?
Because I was experiencing this with probably 25-35k on the odometer.

[Athseef]

Originally Posted by ejm3

Thanks Frank, I'll talk to my dealership.

How many miles before the walnut blast becomes necessary?
Because I was experiencing this with probably 25-35k on the odometer.

mine was at 50,000 miles when it was done, and it obviously needed it. It probably depends on your driving style, and the mods on the car as well. Mine was bone stock.

[mackeroni]

I thought the walnut blasting was only necessary for the N54 engines.

The first thing I would have tried...before going to the dealer...is to run a couple of tanks of the highest quality gas you can find (e.g., Exxon, Mobil, BP, Shell) with Chevron Techron Fuel System Cleaner added to increase the detergent content. There is a lot of bad gas out there, and if you fill up at a lot of random stations or use bargain gas, your valves could be really cruddy. Plus, it seems like you don't drive a lot. Gas can get pretty skunky as it ages in your tank. And worse, the gasoline in your injection system can leave a lacquer behind as it slowly evaporates in your garage.

Peace

[Esteban]

Originally Posted by mackeroni

I thought the walnut blasting was only necessary for the N54 engines.

I think walnut blasting must be done earlier for N54s but eventually will need to be done on N55s as well. Could be wrong but that's my understanding.

[50shadesofhockenheim]

I wanted to update my DCT but the dealer told me it could break a module in my car and basically make my car unusable

[ejm3]

I have been running a can of Techtron every once in a while so maybe that's why I haven't had the problem recently.

I assumed that all direct injection cars would eventually need to have carbon cleared out, not just BMW's.

[quicksilver3121]

Hey Frank, I think I actually met you at one of the Bucks County meet ups, unless there's another guy with a Black Dinan 135 in Bucks county. I had the embarrassingly dirty LeMans Blue 135.

Have you checked for a boost leak? This started happening to me out of the blue 2 weeks ago... I thought it was due to the software issues that I've seen everyone complain about (it's more an issue with the N55/DCT combo from what I've seen). I brought it in for software updates (along with a tranny reseal) and they found that my chargepipe had disconnected from the intercooler.

I still went through with the software update since I found the DCT clutch lag annoying when coming to a rolling stop, car feels great now. While the idle stagger was way worse with the boost leak, I always had a minor idle fluctuation when coming to a stop... It would typically just climb up and settle back down once, the boost leak made this happen over and over and the car would borderline stall before it revved up. Everything is working perfectly since the update.

Hope the software update worked well for you!

[Lucky1]

Try pulling a code using a scan tool or app like Carly for BMW? I used it to diagnose a similar problem and it turned out to be a faulty crankshaft position sensor. Saved $177 CAD on diagnostic charges which was approximately the cost to get Carly and the wi-fi OBD II adapter.

[PhillyfaanM3]

Originally Posted by quicksilver3121

Hey Frank, I think I actually met you at one of the Bucks County meet ups, unless there's another guy with a Black Dinan 135 in Bucks county. I had the embarrassingly dirty LeMans Blue 135.

Have you checked for a boost leak? This started happening to me out of the blue 2 weeks ago... I thought it was due to the software issues that I've seen everyone complain about (it's more an issue with the N55/DCT combo from what I've seen). I brought it in for software updates (along with a tranny reseal) and they found that my chargepipe had disconnected from the intercooler.

I still went through with the software update since I found the DCT clutch lag annoying when coming to a rolling stop, car feels great now. While the idle stagger was way worse with the boost leak, I always had a minor idle fluctuation when coming to a stop... It would typically just climb up and settle back down once, the boost leak made this happen over and over and the car would borderline stall before it revved up. Everything is working perfectly since the update.

Hope the software update worked well for you!

Hey Man,
Thanks for reconnecting. I don't think there's another Blk Dinan 135i in Bucks county or the Phila. area.

In regards to the boost leak, interesting. I have the P3 gauge and would assume that a boost leak would be reflected as a code and/or inconsistent boost pressure and I had neither of these readings from the P3.

Also, i have the manual and not the DCT, most of the examples of this were w DCT.

I dropped it off for the TSB and should have it back tomorrow. I'll try to provide an update once I get it back.

[PhillyfaanM3]

Originally Posted by Lucky1

Try pulling a code using a scan tool or app like Carly for BMW? I used it to diagnose a similar problem and it turned out to be a faulty crankshaft position sensor. Saved $177 CAD on diagnostic charges which was approximately the cost to get Carly and the wi-fi OBD II adapter.

I have the P3 gauge which reads codes and currently it's not reflecting any codes.

[Dylanize]

Originally Posted by Frank 135i Vert

Hey Man,
Thanks for reconnecting. I don't think there's another Blk Dinan 135i in Bucks county or the Phila. area.

In regards to the boost leak, interesting. I have the P3 gauge and would assume that a boost leak would be reflected as a code and/or inconsistent boost pressure and I had neither of these readings from the P3.

Also, i have the manual and not the DCT, most of the examples of this were w DCT.

I dropped it off for the TSB and should have it back tomorrow. I'll try to provide an update once I get it back.

Hi Frank, It'd be great if you can post a pic of your service invoice if it says anything specific about the SIB or something along those lines.

THanks!

[PhillyfaanM3]

Originally Posted by Dylanize

Hi Frank, It'd be great if you can post a pic of your service invoice if it says anything specific about the SIB or something along those lines.

THanks!

So...got the car back. Can't really tell the difference yet as my rev issue was intermittent. But the SIB is 120912. Hope that helps.

[50shadesofhockenheim]

Originally Posted by Frank 135i Vert

So...got the car back. Can't really tell the difference yet as my rev issue was intermittent. But the SIB is 120912. Hope that helps.

I thought it's supposed to be 12 15 14

[quicksilver3121]

I think 12 15 14 is specific to DCT. Frank 135i Vert has 6MT

[PhillyfaanM3]

That's correct, I have the 6mt.