07 S6 - VERY rough cold start. BAD Misfires at idle and under load

A6 All/ S6 All
#11

Update:

I was about to order a new oil separator when I thought it may make sense to inspect the one in the car first. I can seal the inlet and blow air through. If it was in need or replacement would it allow for air to pass through? Not sure how to test this. Should I just buy another?

I was looking for vacuum leaks and found that the Throttle body is leaking. Top left mounting position seems stripped/bending/cracking not allowing snug fit to the intake. You can hear and feel air being sucked in here post TB. I know this wouldn’t account for the crankcase vacuum issue, though it could be to blame for the lean codes? Short of a new intake housing I could possibly get a longer bolt and slip a nut on the back side to pull it together tightly.

Video: https://www.flickr.com/photos/14022792@N06/23060470379/in/album-72157661283835280/
Photo:https://www.flickr.com/photos/14022792@N06/23428448595/in/album-72157661283835280/
https://www.flickr.com/photos/14022792@N06/23060470799/in/album-72157661283835280/

Video of crankcase suction: https://www.flickr.com/photos/14022792@N06/23132682480/in/album-72157661283835280/

I did see what appears to be a hairline crack in the intake manifold. Doesn’t appear to be sucking air at all though:
https://www.flickr.com/photos/14022792@N06/23428448415/in/album-72157661283835280/

Without knowing for sure how to test the oil separator should I order one? Could it be post separator hose under the intake manifold?

#12

If you think there is a vac leak. Try spraying starter fluid in the area that you think the leak is coming from. If the motor is pulling in the starter fluid due to a vac leak the starter fluid will act as a secondary fuel and you will hear the rpm rise. Its a good start

#13

Thank you JRach and JimmyBones for the replies. All very helpful. I will be further inspecting the breather hose.

I finally got a hold of the Audi dealer in Indiana that had the car before I brought it home. They did in fact replace the oil separator, so that should in theory be OK.

I’m just not quite sure whats going on. Started the car up and let it idle for 10 min or so, rough idle to start. Rough going down the road to my local grocery store (5 miles) under load with minimal throttle. Car sat for 45 min. On the way home things felt much more normal and I was able to go WOT without any hesitation or flashing CEL.

Cleared codes after getting home and went out for a spirited drive. I basically threw everything I could at it. low RPM WOT pulls, standing to top of 3rd flat out… no CEL. Still settled into an idle with misfires but not violent. I pulled the codes and things look much better than before.

We’ll see how it starts and runs after a cold night. #3 was the coil with oil. I’m fairly sure I’ll get a flashing CEL. I’ll need to tighten up or seal that leak post MAF at the TB. That may calm the cold idle issue.

Next step is looking for any other vac leaks. Will then pull the intake manifold and inspect the lower hoses of the oil separator leading to the check valve. If #3 and #8 are consistent with misfires I’ll most likely have two fuel injectors to install while the manifold is off.

What could cause such a drastic change in operation at warmer engine temps??

3 Faults Found:
000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 -
Freeze Frame:
Fault Status: 01101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 154783 km
Time Indication: 0
Date: 2015.11.30
Time: 18:33:37

         Freeze Frame:
                RPM: 1715 /min
                Load: 37.6 %
                Speed: 34.0 km/h
                Temperature: 84.0°C
                Temperature: 31.0°C
                Absolute Pres.: 970.0 mbar
                Voltage: 13.970 V

000771 - Cylinder 3
P0303 - 008 - Misfire Detected
Freeze Frame:
Fault Status: 01101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 154783 km
Time Indication: 0
Date: 2015.11.30
Time: 18:33:37

         Freeze Frame:
                RPM: 1715 /min
                Load: 37.6 %
                Speed: 34.0 km/h
                Temperature: 84.0°C
                Temperature: 31.0°C
                Absolute Pres.: 970.0 mbar
                Voltage: 13.970 V

000776 - Cylinder 8
P0308 - 008 - Misfire Detected
Freeze Frame:
Fault Status: 01101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 154783 km
Time Indication: 0
Date: 2015.11.30
Time: 18:33:37

         Freeze Frame:
                RPM: 1715 /min
                Load: 37.6 %
                Speed: 34.0 km/h
                Temperature: 84.0°C
                Temperature: 31.0°C
                Absolute Pres.: 970.0 mbar
                Voltage: 13.970 V
#14

Your codes are for missfires at part throttle and part load. When you see that and you dont have any fuel codes its best to get agressive with a fuel injection cleaner. I would start putting in fuel injector cleaner every time you fill up the car.

As long as your cyl 8 and cyl 3 plugs and coil packs are replaced there shouldnt be any issues with those

#15

I haven’t started the car since pulling the codes on Monday. I’ll be taking it out later this morning so we’ll see how the cold start is. I may use a small strip of RTV if I have it to seal up the TB leak before starting.

Is there a specific treatment you recommend? I’ve only used Seafoam in the past. OK to use a can on less than a full tank to be more aggressive?

#16

So I’m getting some where… New coils were put in, but the car was still running very rough the first few cold starts. Once warmed up it was much better.

Misfires on 3/8 last I checked. Nothing hard enough to throw a CEL.

I laid a thin bead of RTV blue advanced along the vac leak I found between the intake plenum and throttle body. Short term solution however that’s fixed a majority of the idle misfires and cleared up the too lean at and off idle codes.

Running much better and very strong compared to where I was last week. Going to clear the codes again and pull them after some driving with the intake leak resolved.

If I still have a part throttle misfire from 3/8 I may need to replace those two injectors. I have another can of seafoam going in the tank today, so hoping that clears things right up.

Thank you all for the help. I’ll keep you posted on the next week or driving.

#17

ok first off the vac leak is a big deal. You need to make sure that is fixed that will cause all kinds of issues. Lean off idle is a big vac leak issue and missfires are going to be a big issue for missfire codes.

Seafoam is good to keep with it.

#18

Agreed. I can’t believe I didn’t find that leak earlier. I’m sure the coil replacement wasn’t entirely necessary. Leak is sealed up for now. It appears the mount on the intake plenum (top left point) is stripped leaving a small gap and a bit cracked. I will try to threat a longer bolt through and use a nut to pull and tighten things up. I’m sure I’ll need a new intake plenum at some point, so I’ll start looking around the web.

The car and myself are much happier campers at the moment.

#19

Thats always good to hear. Nice job getting to the bottom of the issue

#20

Reviving the topic from the dead!!!

Just got the car back from the shop. They did the valve cover gaskets, spark plugs, and some other stuff.

Still has misfires, and all the symptoms of a bad air oil separator. I happen to have a brand new one sitting here, that I ordered awhile back when someone on AR posted a cheap link on amazon. Now, all I need is a writeup DIY install.

Does anyone have a step-by-step DIY AOS install for the v10 S6?

#21

These things are horrible… I cannot believe Audi gets away with using such an inferior part on such an expensive engine. End rant.

This is actually a pretty simple job, but given the amount of space allotted it’s challenging in the sense that you’re basically taking out one screw completely blind.

There is a bracket I believe that goes from the intake to the oil separator that needs to be removed, both are t30 torx screws, if I recall correctly.

From there disconnect the breather hose from the side of the oil separator as well as the driver’s side valve cover. Just be careful not to damage it as overtime they get brittle and I think they are upwards of $200 to replace them.

From there you will need to use a t30 bit to get the top and bottom screws off of the oil separator. I prefer to use something like this in order to get them started. Once loosened it’s easier to just do them by hand. Be careful not to drop the bottom one! I wedge an old rag in between the firewall and the engine in order to (hopefully) catch it in the event that it falls.

Lastly there is the oil return line from the bottom of the separator that leads back to the top of the block. That will need to be removed from the old one and put on to the new one. Might as well use a new hose clamp while you’re at it.

Installing is essentially the reverse. Word of caution: do not overly force the new one in to the port! The oil separator adapter that links it to the lower intake manifold is only secured by ONE bolt and because it’s very soft it is easy to strip/break the mounting point and you will have to remove the entire intake in order to (hopefully) re-tap the fouled up screw hole. If you’re having trouble coaxing it in, use the smallest amount of silicone spray/sil-glyde to provide a little bit of lubrication. I say smallest amount possible because you really don’t want that getting sucked into a combustion chamber.

Hopefully this helps! Again, it’s a pretty straight forward job that just requires some patience and funky hand work in order to coax the bottom t30 screw out!

Keep us posted!

#22

Thanks for the writeup, man! You described it very well. The hardest part was finding tools that would fit in between the firewall and the part, and also accessing the lower bolt.

Unfortunately, did not solve my issues. Back to the drawing board…

#23

Check the suction jet pump. $27CAD part on my car that has caused so many issues for me.

Part number 078 133 753A (taken right from the part) Will be installing tonight.

I’ve had random misfires and unable to find any other leaks anywhere, but seems that the pump has failed and is bleeding off vacuum somehow.

You can test this if you pinch the hose leading up to it… if the car stops misfiring this could be the issue.

It’s located on the passenger side near the passenger side throttle body. Just follow the hose.

Google the part number and you’ll see the item.

I will report back tonight after I install mine, but wouldn’t be surprised if this is your issue.

#24

thanks for the tip…let me know how it goes

#25

Glad it made sense and you were able to follow it!

For what it’s worth I had a semi-leaking suction jet pump but did not have misfires associated with it. It’s a pretty cheap and easy part to swap out so it’s not the end of the world if it doesn’t correct the problem. Furthermore, I would suspect that a complete failure of the suction jet pump could potentially cause the car to lose breaking capabilities, so certainly worth the piece of mind.

#26

Replace suction jet pump and got rid of higher rpm stumble, but must have a leak somewhere near the intake plentum… deal with that tomorrow.

Just odd, and maybe very coincidental that it’s happening now.

I had done the carbon clean in May, changed plugs, coils, valve cover gaskets, added intake spacers and car ran like a champ.

2 month after that (last week) started misfiring. Same codes and random cylinder as OP.

I’ll check a few more things and report back… very frustrating. And likely avoiding the inevitable need for injectors… just seems weird for 4 or 5 cylinders to misfire over one weekend from having none.

#27

Damn, that is rough. When the carbon cleaning was done, did you have the [urlhttps://jhmotorsports.com/shop/catalog/vent-hose-crank-case-to-maf-hose-oem-for-s6-s8-52l-fsi-v10-p-3994.html?cPath=0_1]vent hose[/url] replaced that sits on top of the crank case? I lucked out and mine appeared to have been replaced fairly recently when I did my carbon cleaning/intake replacement/injectors, but I believe that is a common issue on our PCV systems and is virtually undetectable without the use of a smoke machine to determine whether or not it’s leaking.

#28

Murph can we get you to make a separate thread for this. If you can post a few easy locational pictures for people. Any time we can fight these misfire monsters and make positive changes it helps out everyone if we can document it. I’m working on a misfire master thread and it helps to have each part and conclusion listed if possible. since your suction pump helped it would be great to have a little info on that from you if you can.

Here is how you post pictures to the site.
http://audirevolution.net/image_uploader.php

#29

Hey Justincredible - I was thinking that too about starting a new thread, but this is related to the OP symptoms now. (I’ll post pics tonight, I know how to post pic, but it’s annoying to upload to imgur, ect and then post here again)

It appears that I also have excessive vacuum in the crankcase, oil cap is difficult to remove now that I’ve replaced the suction jet pump, and removal of oil cap causes serious stumble and stalling from the engine…

So I will replace the oil separator (even if it’s only 2 months old) and see if that helps.

I will do some logging too, I need to also check out O2 sensor readings and mass air sensor voltages to eliminate any other issues.

I will post an update when I get that done.

#30

Sweet! I would be interested to hear what your MAF readings are at WOT. I am only able to achieve around 155/160g/s at WOT from both MAFs on my s6, giving me a total of about 310 g/s at WOT.

My research leads me to believe that at WOT we should be seeing a combined total of around 350 g/s (170 - 175 per side) but I literally could not locate a basis for comparison so this would be interesting.