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70 Posts
Discussion Starter · #1 ·
(Please advise if there is a better section for this; I believe this is the most appropriate)


** There’s a lot of text here. If you don’t want to read it all, watch the BEFORE video posted below. It shows the carbon buildup very clearly **

After countless hours of research on this topic of carbon buildup in (specifically) the 4.2 BAR FSI engines, I was unable to come up with any concrete answers (this post HERE is about the best reference I’ve come up with). There's plenty of information on 2.0t engines, as well as some of the V6 FSI engines, but other than the RS4 application of the 4.2 FSI, very little. I'm not going to get into speculating why or how this issue is what it is.

My opinion? It's something that needs to be addressed at regular (albeit probably pretty spaced out) intervals. I did mine at 100k miles (~160k KM). Since it’s hard to pin down exactly what causes the buildup, it’s also hard to specify an exact recommended service interval. I would say every 100 000 miles at most.

There are a few products that have claimed to fix this issue without removing the intake manifold and manually cleaning the intake ports & valves, but they've pretty much been 100% debunked as not really doing anything.


  • Some reference footage and pictures of the buildup I found in my engine, with around 100 000 miles. As stated in the video, I am the third owner and thus don’t know much about how this vehicle was driven before me.
  • Some suggestions on how to clean the ports (see video)
  • Feedback on the process and results


  • A theory on why the buildup occurs (I do have a couple but nothing I can substantiate)
  • A solution to prevent the buildup (most of my reading has turned up that catch cans do NOT make any noticeable reduction in deposits)
  • A step-by-step tutorial on how to remove the intake manifold and clean the ports (I can post a writeup for intake manifold removal if there isn’t anything out there already, although I didn’t take any pictures along the way)

To hopefully make things easier, I have named the pictures 1.jpg through 7.jpg and will reference them as such.

I decided to pull my intake manifold on Saturday morning to inspect and clean my intake ports if necessary. The actual removal of the manifold took me around 3 hours, as I did it without any sort of guide. It’s fairly straightforward, although it’s certainly tight in some areas.

Pictures 1-3 show the buildup I found. Distribution was fairly even; no cylinder seemed to be plugged up more than another. I would say that the buildup ranged from around 1mm thick on most of the port walls, to 3mm, maybe 4mm around the valve stems. Pretty bad.

Cleaning was pretty straightforward, although time consuming. I discussed most of what I did in the AFTER video below, so I’m not going to reiterate that here.

The BEFORE video is probably the one of most interest to most people here since it demonstrates the buildup you might expect for an engine with around 100k miles. As I mentioned above, and in the video, I am the third owner. I do not know if the ports were cleaned before, however I highly doubt it (the previous owner who has had it since ~50k miles ish didn’t indicate that any major service of any kind was performed on the Touareg.

Pictures 4 & 5 show what the ports and dividers should look like when cleaned (of course this depends on how fussy you want to be with cleaning).

For those curious, pictures 6 & 7 are what the inside of the intake manifold looks like. As you can probably imagine, it’s a bit tricky to separate the two halves. I don’t know that I would split the manifold if I did this job again, since there really wasn’t any buildup anywhere other than the flaps that are directly above the intake ports. If you’re careful, you should be able to clean them without dropping anything into the depths of the manifold where it could potentially cause harm. I would, at the very least, clean the backside of the flaps a bit, just so they don’t start sticking down the road.

The verdict?

The 4.2 FSI V8 engines in the Touaregs/Q7 ARE affected by carbon buildup in the intake ports. Maybe not as bad as some RS4s you may have seen, but still pretty bad. So for those who have been asking the question, these are some pictures for you to look at.

Butt-dyno results?

The engine never exhibited any stuttering, rough idle, misfiring, or any codes prior to this cleaning. It ran pretty well. However, after the cleaning, I noticed the engine pulls much harder after ~4000 RPM. Prior to cleaning, the engine pulled well but felt somewhat “flat” through the whole power band. Overall I wouldn’t say it’s a super night and day difference, but I did notice an improvement.

Fuel economy? Throttle response?

I’ll have to drive around for some time before I can comment on fuel economy. Throttle response is improved somewhat, but I think that has more to do with the throttle/transmission adaptation reset since I had the battery disconnected during the cleaning.

Other thoughts?

  1. I would certainly recommend anyone who has a Touareg with over 100 000 miles to definitely consider an intake port cleaning. I can’t guarantee what you’ll find, but I’m thinking that most engines are pretty gummed up by that point, as mine was.
  2. As I discussed in the video, I reused my intake manifold gaskets. So far, so good. Take that as you will; I’m certainly not recommending that anyone reuse theirs, but depending on the shape they’re in it might be an option.
  3. Rather than try and prescribe a fixed interval, I would suggest you pull your intake manifold and assess the buildup. Some engines may be worse than others. In my case, I think I’ll wait another 100k miles to clean it again. However, you may find that a 50k mile interval is warranted. It’s impossible to predict this sort of thing without seeing what’s in there.
  4. I do not know if VR6s are affected by this, or to what extent, as I do not own one. I am only familiar with the 4.2 and 2.0t (my mother’s car, which I have not cleaned yet).
  5. Extending on point 3, every engine is different. Speaking of 2.0t engines, some seem to be prone to issues every 40-50k miles, while others go well over 100k without so much as a misfire. Don’t assume that what one person finds in their ports will be what’s in yours. There are far too many variables involved in this issue.

So there you have it. I hope at least a few people will benefit from my findings. Again, my intent with this post & videos is to shed some light on how this issue affects these Touaregs. They’re getting to the age where people like myself are picking them up second or third hand, with higher miles, where these types of issues need to be addressed.





70 Posts
Discussion Starter · #3 ·
Yeah, 50 000 seemed to be the magic number from what I found too. It's hard to say what effects the differences in the RS4 and basic 4.2 have on the carbon buildup. Hopefully some more people can post their findings when they have the cleaning done (yourself included) so we can possibly figure out the general trend with these particular engines.

$500 sounds pretty reasonable, too (assuming you're talking about your Touareg and not the a4). I figure if I had to do it again, I could do the whole job in 6-8 hours. ~2-3 for manifold removal and reinstall, and the rest for cleaning. I'm sure there are better and faster methods of cleaning than what I did.

70 Posts
Discussion Starter · #6 ·
Have you read this thread?

There aren't many V8 FSI Touaregs out there. 2007's came out mid year and 2009 V8's were shipped here for VW corporate employees. That left 2008 and most were VR6 models with some V8's and a handful of V10 TDI's.

The RS4, like the R8 is a more high revving engine (redline 8,000 RPM) and since they are performance cars, I think their drivers tend to rev them more than a SUV. This leads me to believe that the Touareg may need to be decarbed more often than the Audi. But that's just my opinion.

The S5 B8 has the same basic motor as ours and JHM has a good write up about their S5 build, check it out. It includes pics of their decarb of the motor.

I'm just wondering if it is worth my time (8-10 hrs) to do it myself. The Audi service rep says they decarb lots of FSI motors. Since Audi makes the 4.2 V8 and my VW dealer sees very few V8's I figure they would be better off doing the work on my 2008 Touareg V8.
First time I'm seeing that thread. Thanks for the link, some good information and pictures in there.

Interesting point on the number of Touaregs out there - when I was searching for mine, I noticed V8 FSIs weren't all that easy to come by. Older non-FSI V8s no problem, but newer not so much. Good to know.

I would tend to agree with you about the RS4/R8 being driver harder and thus staying cleaner, but they seem to have MORE issues than the basic V8 applications do. I've read of a ton of issues with RS4s misfiring and whatnot, yet Touaregs/Q7s don't turn up at all in my searches. I'll have to do some more reading on the S5 (and JHMs build as you mentioned) and similar, since it seems to be more affected than the Touaregs. Who knows, maybe driving them harder in fact makes the problem worse? Or that most Touareg owners don't drive them hard enough regularly to notice? Of course there's always the fact that not everyone is going to make a post about it on an internet forum even if they are having issues.

For the cleaning I would agree that Audi would probably be more familiar with the issue. It's really not a bad weekend project if you're into that sort of thing.

Install a good catch can to minimise this.
As mentioned in the OP, there's little evidence supporting this. A few people have installed catch cans with no improvement in buildup. For example, see here (4th bold point): Carbon Buildup 101 - VW GTI MKVI Forum / VW Golf R Forum / VW Golf MKVI Forum / VW GTI Forum -

70 Posts
Discussion Starter · #10 ·
Seems like the V8 FSI CCV system is a fairly robust setup. Deleting could/would reduce but likely not eliminate the carbon issues.
Info on page 12 at
Not sure if anyone has completely disconnected the system, but you would think a good catch can would at least make a pretty decent impact.

It would seem that the factory PCV filtering system (cyclones and whatnot) would be more effective than a catch can anyways.

Probably a dumb question but does using "TOP TIER" additized fuel play any role in helping reduce or slow down the rate of carbon buildup?
I disagree. While it may have some small effect, I haven't yet found any evidence suggesting it makes any worthwhile difference with respect to this issue. Initially Audi cited poor fuel economy in North America as one of the root causes, but carbon buildup is not limited to the NA market; people all over the world are having the same issues.

Audi 2.0 TFSi tuning & Carbon build up issue

Audi FSI Engine Carbon Build-up Megathread

Is Carbon Buildup a Problem With Direct-Injection Engines? » News

Furthermore, from what I have read, the newer engines (ie. 3.0TFSI) do not have nearly as many issues with carbon buildup. Clearly there are other factors at play. It also seems that more VW/Audi engines are affected than other makes' DI engines.

Right now the most probable explanations are a) too much intake/exhaust valve overlap allowing exhaust gases into the intake port, both heating and bringing contaminants into the intake ports, and b) poorly designed valve stem seals not sealing properly, allowing excessive oil onto the back of the valve

70 Posts
Discussion Starter · #18 ·
Some more information (including a patent by VW, detailing the sources of the issue): Q5 FSI Carbon Build-up - AudiWorld Forums

It would seem the internal EGR is the main culprit. Generally speaking, PCV systems will only result in a thin oil film on the intake system (see the OP for the pictures I posted of the inside of the intake manifold - this is what you would expect to find as a result of oil due to PCV). The formation of carbon, I think, is more related to the elevated temperature due to the internal EGR. The oil vapor alone shouldn't result in buildup, but combined with hot exhaust gases reversing momentarily into the intake port will essentially bake the oil onto the walls/valve, resulting in carbon.

So even if additives are effective in removing carbon in the cylinder, I doubt they would have much effect since the EGR (in this case, a simple momentary exhaust gas reversion from the cylinder into the intake port) is recirculating an already-combusted fuel/air mixture. Unless the additives (BG 44k, or detergents found in top tier gasoline, etc.) survive the combustion event in sufficient quantites, AND they actually make it into the portion of gases recirculated during the EGR event, I doubt they'll have any practical effect.

The patent linked in the post I linked to also mentions intentionally leaky valve seals (assuming the technology discussed in the patent was actually applied to these engines), so unless you replaced the valve stem seals with redesigned ones, you'll always have that as a source of oil even if you seal the PCV vapors off 100%.
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