How do I know if I need a carbon clean?

[TS811]

I've had my B7 RS4 Avant for a year now, and have taken it from 90k to 95k (kilometers). Besides a throttle body replacement when I got it, everything has been working perfectly.

I don't know too much about the history of the car. It seems like it was daily driven for its first few years and then only occasionally for the past decade. I have Audi dealer invoices for maintenance since about 2016 so I know it's had regular garage visits, including a DRC replacement, but no reports of carbon cleaning.

I asked the Audi dealer if I should do it but they said it isn't necessary. On the other hand everyone online says it's one the the key things to make sure has been done when getting one. So, how do I know if my car needs it? Will there be misfires? Will I get a CEL? Any other symptoms? If it's just down on power, I couldn't care less, but if it can cause damage then I'd rather get it done.

Also, I keep hearing about a B7 RS4 owners WhatsApp group, can anyone share an invitation to that?

Thanks in advance!

[JamesBaby]

It will be down on power significantly, and possibly not as good MPG. That's about it.
If it somehow gets incredibly blocked up then yes you could have running issues but then you would know about it.

Get on the Facebook "Audi RS4 B7 Owners" club and I believe there is a wider "RS4OC (UK)" club. One if not both have some kind of chat group as well.

[JRC1]

It will always need doing, that's the brutal reality. MRC who are a specialist tuner in the UK told me that as soon as you drive away from having a carbon clean, it will slowly start to build up again. So you either forget about it and just enjoy the car, or you let it do your head in and get it done every 2 years. But it won't cause any damage if it's not cleaned.

I've seen RS4's as low as 290bhp if they've never had a carbon clean, which is just crazy. Not unusual at all for cars to typically be 30-50bhp down on power in between cleans. So up to you - but if you drive a mapped and freshly cleaned car it will feel like a different RS4 compared to an un-mapped and un-cleaned one.

Audi dealers don't have much of a clue about these cars and they certainly won't advise you properly regarding a carbon clean.

[TS811]

Thanks!

I'm not too concerned at the moment, the engine runs great, probably not making 420bhp but that's fine. Maybe one day!

Also, is there a certain driving style which is more likely to result in carbon buildup? I put 3-5k miles per year on the car, 60-70% of which is highway.

[js47]

It pretty much always needs a carbon clean, though I do not think anything bad will happen if you put it off. Besides the flap screws shaking loose, but I am not sure how common that issue actually is.

I highly recommend doing it. It is a completely different car after having it done. I scored 346 horsepower on the dyno before cleaning, and now it is at 423.

I've heard that "easy" driving builds the carbon up faster than high-rev spirited driving, but all driving will build it up.

[highrise]

Totally worth doing if you don't know when it was last done. I went from 360 to 434 with a clean and a bit of a remap, felt amazing.

[JRC1]

As others have said, if you do get a clean then worth getting a Stage 2 map and deflap of the manifold at this point too. The flap screws do shake loose. Not overly common, but I've heard multiple instances of it happening over the years, and then it is more than likely a new engine. I'm sure the power figures quoted above will tempt you. Mine made 450bhp after a clean and a map, but I'm not running any cats so will always make a bit more power. Anything 420 and above will feel amazing frankly - you could well be in the mid 300's at the moment.

[TS811]

My priority is more on reliability and keeping my car in good condition. I'm considering the de-flap as I hear there's a risk to that (but how common really?).

Would a carbon clean give the engine more low-end torque? That's the only area where I feel it's missing a bit.

I live in Switzerland so more power will just end up putting me in jail. I just like the sound of the car and I'm happy if it doesn't go too fast while I'm enjoying it!

[js47]

Regarding the deflap, I would not recommend it in Switzerland. My car runs a little rough anytime it is below around 10C ambient (only for a few minutes until the motor warms up). Luckily it rarely gets colder than that in the UK. A good alternative to deflapping is loctite on the screws — that's what I'd do if I were to do it again.

Regarding torques, I went from 393 Nm before carbon cleaning to 440 Nm after.

[JRC1]

My priority is more on reliability and keeping my car in good condition. I'm considering the de-flap as I hear there's a risk to that (but how common really?).

Would a carbon clean give the engine more low-end torque? That's the only area where I feel it's missing a bit.

I live in Switzerland so more power will just end up putting me in jail. I just like the sound of the car and I'm happy if it doesn't go too fast while I'm enjoying it!

Have a read of this thread here: viewtopic.php?f=35&t=144611&p=977372

You will gain more torque with a carbon clean. There are zero negatives of having a carbon clean done. There are some negatives of deflapping the manifold, but many feel these are outweighed by the positives.