RS5 - idle RPM flare (surge) when coming to a stop

I have been noticing this recently on my (bone-stock) 2013 RS5. I have owned it for about 2 months, currently with just under 80k KM (50k miles). I have been searching far and wide to try to find any discussions or even TSB’s on the phenomenon, but struggled just to get the right words to describe it clearly. However I just hit on a thread at Audizine started in 2013 that seems to be similar/same issue. I will share the link here. I hope someone might know more on this, normal or something I can “fix”? RS5 idle flare-up link For me, now that I am paying attention, this is happening in residental driving, slow speeds, and maybe before the car is fully warmed up. BUT… NOT EVERY STOP SIGN… why?

As I putter along at 25-40 mph, and start coasting to a gentle stop, RPM drops down towards 1000rpm and a bit below, then I assume the clutches disengage in the DSG, and the idle lifts up to about 12-1400rpm, holds for a second or two and then will drop down towards 800rpm or so. It’s that lift/float up to 1200 or so that just does not seem right. The car is not stone cold and the temp gauge is already registering something.

Could it be there are some software updates that tame this, that perhaps the original owner never noticed or complained about during the warranty period?

I can elaborate more if my explanation is not clear enough, and this weekend I have a good hour-long highway drive to do, so I can attempt to reproduce under fully “hot” conditions as well as the warm-up residential ones.

I don’t use the AC much in the city, and when I do it is using the recycling. This is a guess but could it be the mechatronic version or the update? Is it in all modes, auto should be able to train (by driving differently)/flash it. It might be a bit lazy.

My idle is at 600 - 650 rpm. Is your idle smooth, what amount of misfiring?

Is it all the time? I might have noticed it in the past occasionally, but definitely long gone now.

Tonto, thanks for your reply. I paid closer attention and agree idle speed without AC is around 650 rpm and maybe 700-750 when AC on. My idle and whole warmup cycle is smooth without any roughness at all.

I tried starting up yesterday evening and again this morning without AC and could not get the “flaring” or raising rpm symptoms to happen. Maybe it is related to having AC always set on, but still is that something that Audi may have “fixed” later in these B8.5 cars? I wish danidoza7 over in audizine had more details in his 1-June-2017 post where he said his Chicago dealer applied some updates that he felt transformed his car… One he said was for ECM (idle up) which catches my attention!

I will continue to test and observe this behaviour to see if it is only AC that seems to cause it.

Mine does the same (2015 model year) and I leave AC set to auto all the time. No other symptoms just a relatively small surge in revs almost just before the car comes to a complete stop then when stopped the revs settle down again. Figured it was the S-Tronic doing its thing. Everything else smooth. My car has had a ECU and TCU tune (in Australia) and they gave the car a full work over before and after with no issues detected and I also have a VCDS and have no error codes.

not to be pessimistic but this is a pre-cursor to the DL501 mechatronic failure issues. (for me at least)

i had 3 failures on my mechatronic unit over past 3 years, 1st time required replacing the whole unit, second one required rebuilding of the solenoid valves, third time required replacement of PCB boards. These things overheat and break very easily. Each time, 2-4 weeks before the failure, the flare-up happens.

i suggest taking the car to an Audi specialist, get the DL501 mechatronic unit taken apart and looked at, do the pressure test on the valves, and get a full service done.

Also, you may want to take some readings on your ATF fluid, transmission oil, control module, etc and see the range of temperatures that they are operating at. I use an OBDEleven bluetooth dongle and do a Live data read of the transmission oil/fluid temperatures to monitor how hot it gets

i have a transmission cooler from Red Mist Racing on the way, hope that solves the overheating issue that is all too common with these transmission mechatronic units

Yes, could it be to cool the transmission down when hotter? Particularly city driving.

Also wash of any insects the cooler aggregate

Thank you for the further replies. Andrew, yes I know the potential for Mechatronic failures in the earlier RS5 DL501 (compared to 2014 & 2015). It will be planned for in the budget :thinking:

Just to reiterate, these observations only seem to be happening on the car when “cold” or well before fully warmed up. Today (~70f) I drove without AC on, and I did experience that “RPM flare” twice, so the AC usage seems NOT to be a direct cause…

Scanned the vehicle yesterday to see if any codes, none in Engine or Transmission modules. And for those who may have very extensive software version knowledge, here are my Engine and Trans module versions: Engine 8T2907560B Hdw: H04 Softw: 0004 and Transmission 8T0927156F Hdw: H01 Softw: 0008

Oh, and yes I have that RMR transmission cooler kit on my shopping list!

UPDATE The issue can and does happen on a fully warmed up engine, so not just within 10 minutes of cold start-up.

This is coming from my latest scan. It seems to say the dealer has updated the software for the transmission as I seem to have version 10, which is running fine.

I have never heard of how this particular software is updated, but I started another thread here with a link to the user manual.

Bear in mind it should adapt based on if you driving habits. Maybe you can reset it also unplugging the battery. I would personally just ignore and live it, hoping it goes away. I never heard of a software update helping with the hardware but I defer to greater knowledge

Address 01: Engine (------CFSA) Labels:. 079-907-560-CFS.clb
Part No SW: 8T2 907 560 HW: 8T1 907 560
Component: 4.2l V8HDZ / H04 0003
Revision: NAH04—
Coding: 1A25003225A6080A3000
Shop #: WSC 06208 000 00000
ASAM Dataset: EV_ECM42FSI0118T2907560 001006
ROD: EV_ECM42FSI0118T2907560.rod
VCID: 79AE14A2D9588643C8D-802C

Address 02: Auto Trans (J217) Labels:| 0B5-927-156.clb
Part No SW: 8T0 927 156 E HW: 0B5 927 156 K
Component: 0B5 42 FSIRdW H03 0010
Revision: --H03—
Coding: 000001
Shop #: WSC 04940 001 00001
ASAM Dataset: EV_TCMDL501021 001015
ROD: EV_TCMDL501021.rod
VCID: 3FDABABA87FC6873B69-806A

I had this and of particular note was the A/C link, mine was definitely more prevalent with the A/C on.
But some hope, mine stopped without any mechatronic failure, I believe it was probably resolved by putting a new battery in the car.
Seems unlikely but a few people on the forum had mentioned Electrical requirements and the car increasing revs to provide a bit more current ?
I’d give it a go or at least get a proper load test done (not just a voltage test) on your battery.
Good luck, it used to annoy the $#!€ out of me

Thanks Durin, that’s good to know. My “surging” is definitely more pronounced when the engine is cold and i don’t really notice it much of any other time. I gave it more attention over last weekend to see if I could make it happen in different circumstances. I also fitted a Transmission mount insert so wanted to see if i could notice much difference with that installed (not much on first impression). Given my car battery is coming up 6 or so years now I might just get it replaced without waiting for it to die and see if that makes a difference to the surging.

Cool it will be interesting to see if the battery resolves it

I had this a year or so back and I changed my battery and it solved it so hopefully it will yours too !

I have a 2014 RS5 Cab, purchased used in Oct of 2020 with 15K miles. I noticed this issue right away. Does not happen all the time and it does not matter if the AC is on or off. Very annoying. Thinking about disconnecting the battery and reconnecting to see if it resets anything. Thoughts?

I changed my battery today. Only had the chance to take it for a short drive but no surge to be seen! Will monitor and report back if I do detect some surge after I have had the chance to drive for a bit longer and in different operating conditions, but initial signs are very good. My battery was definitely on the way out (was reading 11.99V after leaving it overnight) and having been in the car since late 2014 I think it was due a new one.

What brand battery did you install?

It is the same dimension as the OEM although the OEM was a Moll EFB and the Varta is an AGM.

A late response but as you can see it’s appearing pretty likely that a new battery resolves this issue, disconnecting won’t fix it, cheers

Awesome, sounding very promising, let us know

Where did you buy the battery from?