EEMan

As noted in an earlier post I just ordered a new allroad. Now I wonder if this is a good idea. I watched a video of a tech cleaning the valves on a VW DI engine. There was a ton of work just getting to and removing the intake manifold. I understand clearly the problem with DI preventing detergents from working and I also know this a problem for all brands of DI. Apparently there is a bit of a fix by increasing valve overlap which was a TSB at some time. I assume this is part of current engines. The best advice I saw was an Italian Tuneup regularly. Obviously the folks on this forum are aware of this and willing to deal with it, but aside from the possible repair costs it seems like the issue would significantly reduce the value of our cars at say 80K miles. Should I just cool my jets and not worry about it?

bob m

I thought Audi had fixed that issue a few years ago? BTW, what is an Italian Tuneup?

EEMan

An Italian Tuneup is driving the car at high rpm for a time to clean things out. I have seen a couple of notes that among VWs the GTIs are less prone to carbon build up because they tend to be driven harder.

snagitseven

There have been several threads discussing carbon deposits on the valves with DI engines. Bottom line is all of them, by virtue of the design, can have excessive carbon build up in time since the fuel ignition does not reach the valves. It's best to change to the best oil available every 5K miles which can slow the deposits down, but not eliminate them. Driving hard won't do it either. Engine performance decreases over time so it's not usually noticeable to most drivers. The process today to clean the valves using crushed walnut shells is not too expensive nor difficult.

CoMeader

I personally wouldn't worry about it. I have an '06 with the first generation of the 2.0 TDI and 151k miles on the clock. I haven't done anything special to it WRT carbon buildup, and it's running just fine.

EEMan

Thanks for the helpful responses. I'll just enjoy my allroad when it comes.

bob m

Huh? Crushed walnut shells? Can you explain?

breadbooze

It's a technique of using a media (sand) blaster with walnut shells to clean intake valves (on DI engines) via removal of the intake manifold. After blasting the shells are vacuumed and manifold reinstalled.

bob m

Thanks. Is this something Audi service can do? I can't imagine it wouldn't be expensive, but I'm guessing. Wouldn't using the best of the top tier gasolines also go a long way in reducing carbon buildup?

snagitseven

Not sure how many Audi dealers have adopted this service. I know mine hasn't as of yet. Some indy shops do it and I believe I've seen it done for about $400-$500. There are also DIY kits if you are so inclined.

In a nutshell (pun intended), the design of DI engines is that the fuel is injected directly into the combustion chamber of each cylinder. As a consequence the fuel injectors are no longer placed before the intake valve, but directly in the cylinder itself. The disadvantage of this is that the regular bathing and cleaning of the intake valves by way of the fuel that they are exposed to, does not happen. The intake valves are only in contact with air or rather blow by gases from the crankcase breathing circuit, in which substantial quantities of fuel and oil can be found. Over time, these lead to deposits of carbonized fuel and oil in the intake tract as well as on the intake valves themselves; this is also referred to as carbonizing (or coking). This is not immediately bad for the engine, but over time can have a detrimental effect on its efficiency. If the valves are heavily carbonized, they may not close properly and symptoms such as a bumpy idle, vibrations and diminished throttle response can be observed; it may also contribute to increased oil consumption. While using Top Tier fuel will certainly help with keeping the cylinders and fuel lines clean, it won't help with keeping the valves clean in a DI engine.

Here's lengthy thread worth the time to read that gets into the weeds on DI engines and valve carbon deposits:

https://www.audiworld.com/forums/a6-...gines-2909914/

Also one on walnut shell valve cleaning of a BMW (similar process for any DI engine):