What could be causing my choppy idle when reversing out of my garage?

[chadillac2000]

I've owned my F10 M5 for a few months now and have had this happen on three different occasions since taking delivery of the car. After a cold start of the car and shifting into reverse to get out of my garage, the idle will become suddenly erratic and has even stalled out before. If I let the car warm up for a few minutes after cold starting before moving it, the problem seems to be non existent. Even when the car has stalled out the one time, no codes were thrown to even check. Car seems to run and drive beautifully otherwise.

Could this be defective or dirty MAFs causing this? Just strange to me that shifting into reverse seems to be when the problem kicks in.

[Chauncey.Bishop]

Originally Posted by chadillac2000

Could this be defective or dirty MAFs causing this? Just strange to me that shifting into reverse seems to be when the problem kicks in.

It's likely, spray them with MAF cleaner and see if your idle improves.

[chadillac2000]

Originally Posted by Chauncey.Bishop

It's likely, spray them with MAF cleaner and see if your idle improves.

I ordered some on Amazon and will be cleaning them when I install my Dinan intake setup soon. I'll report back with whether it helps or not.

[SmokinJoe]

So I have the same issue though my vehicle has never stalled. Just unstable idle. Problem seems to be worse when it’s cold out. Think a lot of it has to do with the colder plugs with less gap. Mine are the same plug but set to .022 gap. I have also heard the throttle actuators being worn can cause this issue. The throttle blades are plastic from what I’ve seen so accelerated wear is possible. With the valvetronic system these cars have I wouldn’t think it would depend on the throttle actuators at idle that much but who knows. The other thing is if you have a cold start delete on top of everything else it may just be too much to have a steady idle when dead cold. If you have BM3 there is a cold idle setting I believe. May be worth a shot. It’s in the map configuration tab I think.
Good luck

[eritF30]

What plugs are in the car currently?

[chadillac2000]

Originally Posted by eritF30

What plugs are in the car currently?

My plugs are OEM with 41K on them. Not sure about the gentleman who posted right before me.

[SmokinJoe]

Originally Posted by chadillac2000

My plugs are OEM with 41K on them. Not sure about the gentleman who posted right before me.

Sorry about that. I scanned through your build thread and thought you installed new plugs but now see that you haven’t put them in yet. I have the NGK 97506.

[chadillac2000]

Originally Posted by SmokinJoe

Sorry about that. I scanned through your build thread and thought you installed new plugs but now see that you haven’t put them in yet. I have the NGK 97506.

Yes, I have a full set of NGK 97506 plugs I plan on installing when I install my catless downpipes and stage 1 tune just as preventative maintenance. At 41,000 miles, the original plugs are probably nearing the end of their usable life, but I doubt plugs are causing this issue. Most issues involving plugs I've encountered on BMWs over the years, especially boosted ones, will pop up under boost under WOT conditions.

This only happens when I start the car cold, and back out of the garage before the cold start has a chance to lower the RPM back down to normal.

I do plan on deleting the cold start once I add downpipes and the BM3 tune, so I'll see how that plays into it, but I'll try the MAF cleaner before anything else. It appears to me like it has more to do with the DCT transmission at this point.

[SmokinJoe]

Do the clutches grab abruptly when you start to creep? I can make mine surge just by turning the power steering. Guess it puts enough load on the motor to start it surging. Clears up quick though. Did this start after changing anything like maybe air filters or anything like that. May want to look at short term fuel trims at idle to. Even if you check them warm it may show something. May be time for Primary O2 sensors also. If you see any discrepancies from bank to bank I would look into sensors for sure. Either way get those maf sensors clean and keep us posted.

[chadillac2000]

Originally Posted by SmokinJoe

Do the clutches grab abruptly when you start to creep? I can make mine surge just by turning the power steering. Guess it puts enough load on the motor to start it surging. Clears up quick though. Did this start after changing anything like maybe air filters or anything like that. May want to look at short term fuel trims at idle to. Even if you check them warm it may show something. May be time for Primary O2 sensors also. If you see any discrepancies from bank to bank I would look into sensors for sure. Either way get those maf sensors clean and keep us posted.

Yes, yes they do in fact. Same deal with the power steering. The majority of the time, it does clear up quickly, but on a few occasions as I've mentioned, it's resulted in nearly stalling -- and one time actually did.

I noticed it happened for the first time only a few weeks after I'd gotten the car when backing out of my garage without waiting 30 seconds or so. I had not messed with anything with the car at that point maintenance related.

I do have the BM3 datalogging at my disposal to monitor fuel trims, so I will look into that. The MAF sensors may be causing it as they seem to be tempermental in these cars from what I've read. The cleaner just got here yesterday, so I'll update this weekend and see if it helps.

[vafan13]

Does it only happen if you reverse during cold start, or still shortly after? The only time I had it go wacky was when I tried to reverse early on in the cold start, when idle revs were sitting in the 1100-1200 range. Although I think I also had to tab the gas to cause it.

And a completely non-rhetorical question: why would a dirty or malfunctioning MAF sensor cause severely unstable idle when starting up cold, but magically cause no problems a few minutes later or any point thereafter?

[chadillac2000]

Originally Posted by vafan13

Does it only happen if you reverse during cold start, or still shortly after? The only time I had it go wacky was when I tried to reverse early on in the cold start, when idle revs were sitting in the 1100-1200 range. Although I think I also had to tab the gas to cause it.

And a completely non-rhetorical question: why would a dirty or malfunctioning MAF sensor cause severely unstable idle when starting up cold, but magically cause no problems a few minutes later or any point thereafter?

Seems to be only after reversing DURING cold start. It just seems strange to me that reversing while in cold start mode would cause a very advanced ECU to malfunction enough to stall the car out. I've done some more research and some people are saying it could have to do with the DCT software on the car, although I haven't explored that theory any further.

And I do not have an answer to your question, but figured cleaning the MAFs would be an easy, cheap thing to check.

[vafan13]

Originally Posted by chadillac2000

Seems to be only after reversing DURING cold start. It just seems strange to me that reversing while in cold start mode would cause a very advanced ECU to malfunction enough to stall the car out. I've done some more research and some people are saying it could have to do with the DCT software on the car, although I haven't explored that theory any further.

And I do not have an answer to your question, but figured cleaning the MAFs would be an easy, cheap thing to check.

Gotcha. It definitely threw me off the one time it did it to me. I think I had given the throttle a little bit of a "punch" to get it in gear, and that hitting the brake and stopping the car stopped it. I'd be curious to know if others could replicate it by doing the same thing. I'd try it again myself (for science), but it's garaged up for the winter now.

I can't recall if there's been another time I actually started backing out during cold start. Both before and after that my practice has always been to give it ~30 seconds (or at minimum until the cold start ends) to start driving on a cold engine, anyways.

P.S. I'm enjoying reading through your 135i build thread