2015 Audi A3 2.0T, 97K miles.
EA888 Gen 3 engine
Mostly highway driving and the owner has a heavy foot.
Oil changes are done every 10k using synthetic and generic filters, but I doubt he uses an Audi spec oil.
No misfires, but it did have a somewhat rough idle at cold start up.
Before - Cyl 1:
View attachment 88366
Unfortunately I forgot to take pictures of the other cylinders before the cleaning was performed. Cylinders 1 and 2 were much cleaner than 3 and 4.
After:
Cylinder 1:
View attachment 88367
Cylinder 2:
View attachment 88368
Cylinder 3:
View attachment 88369
Cylinder 4:
View attachment 88370
All of the carbon was soft and sticky. I think solvent may have been almost as effective as walnut blasting.
I gave cylinders 1 and 2 a follow-up cleaning after taking those pictures. I found some leftover carbon on the backside of the stem.
The process is fairly quick once the intake manifold is removed. Set the cylinder to TDC and make sure the intake valves are closed. Using a pick, carefully “pull off” the sticky pieces of carbon deposit from the back side of the valve stem and the edge of the valve. It takes well under 30 seconds of blasting, per valve, to remove most of the debris. Then, I blow out the remaining media with shop air, scrape off any large or stubborn bits that were missed, and follow up with another quick blast (few seconds). At least for this vehicle, that approach got the intakes valves near perfect.
I bought this machine for the job:
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This is the factory BMW tool for intake valve cleaning. I have never used the HF equivalent, but this BMW tool works extremely well. The bad news is that it consumes an absurd amount of media. I went thru almost 50 lbs of the HF Walnut media (fine grade). And I only blasted each cylinder for 30-45 seconds total.
Cleaning the intake valves does appear to have resolved the rough idle and has greatly improved the throttle response. I recognize that these are subjective improvements, not objective. Although it was nice to do, cleaning the valves was not entirely necessary.