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View Full Version : Odd engine issue with 2010 S5 4.2 V8



mj1
11-17-2014, 06:22 PM
Let's see if any Audi mechanics can help me diagnose this issue I had last week...

So, suddenly one day I go to drive the car, and between 3k - 4k RPMs there is a tremendous loss of power and the engine sound is deep and hollow, not throaty like before, just hollow and empty. Normally, at that RPM interval is where I get a little power surge as the big V8 just starts to get going. Instead of a power surge, the engine now struggles to convert power so much so that it almost feels like it's vibrating. This is much worse in the morning when the engine is cold, than after the engine is warm. When warm it is still very noticeable though, and it's nowhere near the power that was there before. My layman's guesses range from insufficient air or fuel to clogged exhaust or vacuum line. However, I should mention that both before 3,000 RPMs and after 4,000 RPMs, the engine pretty much drives like normal.

Here's where this gets even stranger... Without doing anything to the car, the problem suddenly went away yesterday, and when I got in the car to drive in the morning it was absolutely fine. Power surge at 3,000 RPMs is back, and the car is back to normal.

I know people like to throw out carbon cleaning on this forum for pretty much every issue, so perhaps useful to state that I had carbon cleaning done about 4,000 miles ago. That, changing the thermostat, and the oil separator, is the only mechanical work performed to date.

Thoughts about what might have happened?
Thanks in advance!

A4-B6
11-17-2014, 06:33 PM
Any codes? my guess would be the intake flaps screwing up but you should take it to a knowledgeable shop.

toononame
11-17-2014, 11:52 PM
You mean the intake flaps in the air box? I always wondered if those really had a function besides making a nice noise when they open up. I wouldn't think they would noticeably rob that much power.

mj1
11-18-2014, 09:22 AM
No codes while I was experiencing the issue, but weeks before the check engine light would come on for a few days, then go away. Finally took it to read the codes, and it was for intermittent sticking of the 'runner control'. So you might be on the right track...