C7.5 Audi S6 Rough Cam Like Idle When Warmed Up and in Park or Neutral

[jh_s6]

Hey guys I’ve been having this rough idle cam like idle only in park and after the engine is roughly 180-210 degrees Fahrenheit (warm) in my C7.5 2018 Audi S6. The car needs to be sitting for a little while until warmed up then it starts making this noise in the video I’ve linked. Apparently both motor mounts were done under warranty when I brought it in and Audi is claiming this is somehow normal. There are 2 or 3 others having this issue and it would be much appreciated if anyone can guide me and the others in the right direction toward solving this annoying issue. I’ve done spark plugs (VAG OEM plugs) all correctly gapped and torqued to spec. Car ran better in general but rough idle is still there. Maybe timing chain? Or something engine to transmission related? Turbos impellers on cold side were checked by Audi and they appeared to be normal. Maybe PCV? No squealing now but a few times on startup in the cold weather did have a slight squeaking for about a min (hasn’t happened in a while). When removing the oil cap idle raises and then starts to run a tiny bit rough and I almost heard a metal noise like something going through the engine. I replicated it in front of an Audi master technician and he claims it’s the valve adjusters switching and is normal. Unfortunately I don’t have a video of that noise and can’t get one because car is currently at Audi for roughly the 5th time (between two dealers). Thank you to anyone who can offer insight or help. https://youtu.be/ggTahn282TE


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[bpd]

I have the same yr and nothing like that on mine.

[jh_s6]

I have the same yr and nothing like that on mine.

Hmm okay. Any way you could pop the oil cap off while videoing it and running and see how much suction the car has and then close it again. Wondering if since I have a lot of vacumn it could be the pcv.


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[Pabla]

Have you scanned your car for codes? If you are having any PCV related issues a code should show up. I popped the cap off my 2018 RS7 and the suction isn't too much, I do also get a slight metallic noise but it goes away soon after the idle increase. In your video it sounds a looks normal to me, my RS7 does the same.

[joserod92]

My 2016 sounds exactly like that, no codes.

[jh_s6]

Have you scanned your car for codes? If you are having any PCV related issues a code should show up. I popped the cap off my 2018 RS7 and the suction isn't too much, I do also get a slight metallic noise but it goes away soon after the idle increase. In your video it sounds a looks normal to me, my RS7 does the same.

Thanks for your replies. Is there any way you guys can check your total misfires per each cylinder using vagcom or obdeleven? If your cars sound the same how it’s rough running then you may be misfiring too like I am. My car didn’t throw any faults or CEL’s but I keep seeing misfires pop up on different cylinders randomly especially when it’s hot and up to temp. Mine are in the several thousands with the highest ones being on cylinders 1,2,5, and 6. The misfires per all 8 cylinders on my 2018 with roughly 49,500 miles are as follows:

Cylinder 1 - 4367
Cylinder 2 - 6430
Cylinder 3 - 3218
Cylinder 4 - 3192
Cylinder 5 - 4576
Cylinder 6 - 6059
Cylinder 7 - 3075
Cylinder 8 - 3565

Cylinders 2 and 6 are the highest misfiring cylinders with 6000+ misfires which to me is certainly not normal.

Would love to see what yours are and what mileage you guys are at.


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[bapmax]

Having literally ALL the same issues with my 2017 S7 and your video is spot on the same exact sound I have. Personally I am 99% sure it is a failing dual mass flywheel unfortunately. Taking mine in to get diagnosed tomorrow and can report back but I am curious if you had anymore updates?

[lees7]

My 2017 just started doing the same after being in for service. 45k. Waiting for them to take a look…

[digdah]

Any update on this guys?

[bapmax]

Shop diagnosed as failing DMF. .

[bapmax]

Following up, my tech and I fell down quite a rabbit hole as it became clear the previous owner made some VERY sketchy repairs after thrashing the car when they owned it e.g., they put an entirely wrong trans in the car, and tuned it to not register launches in memory. I started by telling my tech about the rough idle, misfires, and rattling when shutting off car and agreed DMF was to blame when he inspected. While in there he noticed a whole lot of other issues. In the end we replaced trans, clutch packs, DMF, and flex plate but the sound/misfires REMAIN.

[jh_s6]

Following up, my tech and I fell down quite a rabbit hole as it became clear the previous owner made some VERY sketchy repairs after thrashing the car when they owned it e.g., they put an entirely wrong trans in the car, and tuned it to not register launches in memory. I started by telling my tech about the rough idle, misfires, and rattling when shutting off car and agreed DMF was to blame when he inspected. While in there he noticed a whole lot of other issues. In the end we replaced trans, clutch packs, DMF, and flex plate but the sound/misfires REMAIN.

Hey any update on this since? Still chasing down this issue another 1700$ in diagnosis out of warranty by a reputable performance shop that said turbos are worn so brought it to Audi and they said turbos seem fine and can’t figure it out. My turbos seem to have a little more side to side shaft play than I’d like to see, or feel is normal, but I’m no expert by any means. In and out I can’t remember whether both were tight but I remember at least one being tight with no front to back movement. Forget whether the other was as well or whether I even checked it with everything going on. Is there anyway you guys with the rough idle and no codes on s6/s7 turbos could let me know if your turbo housings look the same as mine and if the shafts have the same play? Saw a YouTube video of turbos that were causing a rough idle with no CEL or anything and the rear impeller was shredded and the other side front impeller just barely scraping. Thanks in advance! I linked a video of me shaking the shafts at the dealership when they tore it all down for me.
https://youtu.be/6aKt5PHAFkY


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[Optimus247]

O2 sensor recall ... or hpfp going soft ...??

[jh_s6]

O2 sensor recall ... or hpfp going soft ...??

I've actually replaced both downstream O2 sensors when I received signal stuck lean codes for each downstream sensor but didn't fix idle at all. The car still idles rough when warm but changing the O2 sensors did remove the codes. Haven't tried HPFPs yet due to fuel pressure aligning perfectly (specified vs actual). I did do the LPFP under the rear seat just in case as a shop suggested but no change in idle. I've tried looking into timing parameters to see if maybe timing may be slightly off but not sure if i've checked the correct values and if these values reveal anything. Maybe someone a bit more knowledgeable can chime in. I've attached an image: https://ibb.co/vkkRdgn

[jh_s6]

Following up, my tech and I fell down quite a rabbit hole as it became clear the previous owner made some VERY sketchy repairs after thrashing the car when they owned it e.g., they put an entirely wrong trans in the car, and tuned it to not register launches in memory. I started by telling my tech about the rough idle, misfires, and rattling when shutting off car and agreed DMF was to blame when he inspected. While in there he noticed a whole lot of other issues. In the end we replaced trans, clutch packs, DMF, and flex plate but the sound/misfires REMAIN.

Hey man any update on fixing the issue at all?


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[jh_s6]

My 2017 just started doing the same after being in for service. 45k. Waiting for them to take a look…

Any update on this since they took a look?


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