LR95S97

The #2 fuel injector failed several months ago, prompting me to have all four replaced.

The shop showed me pictures of the carbon build up, and they where somewhat surprised (considering only had 18,000 miles at time of repair). They chemically removed some (not all) of the deposits.

As SloopJohnB@mac.com (read all his post - he KNOWS his stuff) said in a recent post, "with DI and EGR and PCV, carbon buildup generally an issue".

Other than putting premium gasoline in the tank, what preventative measure can be taken to minimize carbon build up?

Conversely, what reactive measure can be taken to remove carbon build up?

rj12

What year do you have? I just got a 2013 and hope it doesn't have this problem. I had a 2006 gs300 before this car and I actually had the carbon build up problem since it has been an issue with direct injection cars. Lexus rebuilt the motor for me for free as long as it was within 9 years. I turned it in to them 3 months before the 9 year mark. They tested it and said they'll need it for a couple weeks. I would have kept the car after but then other things started to occur and I had wanted a newer car anyway.

LR95S97

I have a 2010.

I am far from an expert, but was told by my mechanic that carbon build-up will occur on any/all DI-Direct Injection engines.

mhblaw

I have a 2013 RS5 with 46k on it. Runs great. What are symptoms of carbon build up?

lmariorod

We (the wife) owned a 3.2 NA '10 Q5 that was known for CB, similar to the 4.2 NA. We never had an issue in 5 years and traded in with 88K.

Our experience was that you needed to drive at operating temp.for an extended period of time and at highway speeds. Too many short trips at 20 to 45 MPH, with minimal time at OP temp. were sure ways to quicker CB.

Also, although gas does no good in preventing eventual CB, TOP TIER, and in our case, mostly Shell V-Power was a must. If it did zero to prevent CB, it did keep your fuel gauge functioning properly, your fuel lines cleaner and therefore your injectors cleaner and less gummed up. Premium gas alone, particularly if its 91 may not be enough.

And although considered by many to be "snake oil" I did pour a bottle of concentrated Techron and VW G17 fuel additive to keep all the mentioned fuel parts clean. Afterall, if you take your car in for rough idling and or sluggishness, they will start with your underperforming injectors and then recommend CB cleaning. Two pricey jobs that could have prevented, (in the case of clogged injectors) or delayed, in the case of CB.

Again. This has been my experience on both our Q5 and S5 others will have very different experiences.

mhblaw

My daily commute to the office is about 6 miles including some freeway at 55 mph, so car always gets warmed up.

rj12

With my Lexus it would seem like it was going to stall when coming to a stop...especially off a freeway. I had 120,000 miles on it. The service adviser told me not to baby the car which I hadn't done anyway. They had told me if you push it hard it would help with pushing the gunk out. I don't know this to be true...that was their response. Luckily they covered the repair with it being 8.5 years old at no cost to me. Had I gone over the 9 years I think they quoted me 7500-8500. I can't remember.

SloopJohnB@mac.com

Reactive: Not much other than clean the CB-affected parts. In the case of intake port/valve deposits, it's remove the intake manifold, ensure the valves are closed, use a walnut shell or other gentle blasting medium combined with a suction device to clean the ports/valve stems. There is at least one DIY media blaster kit available from bavauto.com:
Welcome to bavauto.com | Media blaster kit - For purchase - Includes media blaster, walnut shell media and Genuine BMW heavy duty aluminum vacuum adapter

Here's another source…they may even have added an adapter that fits Audi engine ports.

I have to laugh at dealers and indy shops that quote thousands of dollars for this job…sure they have to amortize their equipment and pay their techs, but their profit margins are outrageous. BMW dealers and indies can do it for around $600 or so.

Another example is a blown spark plug thread….no Audi dealer is going to do a threadsert when they can charge $3K for a new head! You can buy the tools and five threadserts for about $225 and repair the stripped spark plug hole yourself with a repair that is about 3X stronger than OEM….all things being equal the aluminum heads should have had inserts in them anyway, much as aluminum holes should have inserts in them rather than just be threaded aluminum (ok, it's aerospace tech but still).
End of rant.

superswiss

Seems like the only way to delay it is to get the engine really hot for a while to burn off the carbon and gunk. Just warming up to operating temp and driving at US highway speeds may not be enough. Regular redlining and hard driving seems to help. Extended road trips where the engine stays hot for a long time is also supposed to help.

Worst seems to be frequent short trips and stop and go commute driving.