Is this symptomatic of RS4 intake carbon buildup?



Hi All,

I am questioning my dealer's diagnosis of intake manifold carbon buildup and wanted to run the case past others here to see what you think.

Symptoms:
Took car in for 75k maintenance, running flawlessly. Pick it up the next morning. Immediately notice excess vibration from the engine at idle, and increasingly strong vibrations when raising revs from idle up to 2krpm. 2krpm and above seems normal. Very noticeable excess vibration under 2krpm.

Park it, bring it back in the next morning. They recognize the problem, but are unable to identify cause. No codes, no broken motor mounts, no misfires. Their theory is perhaps the 75k injector cleaning dislodged some carbon, causing the rough idle and strong vibrations at 2krpm.

What do you think?

I was under the impression that in a direct-injection engine, that injector cleaning would not even touch any carbon that may have built up in the intake. What would cause such a marked difference between a completely smooth-running engine the day prior?

Background:
2nd owner. Purchased at 45k miles. 95% of fill ups from Chevron or Shell. Regularly driven hard (wind out 1-2-3rd gear on daily commutes).

Thanks for your help!
Jonathan