| BrianG |
08-01-2007 07:10 AM |
Engine startup rattle problem. Possible resolution....
I've complained about an engine rattle that happens about 50% of the time for just a couple seconds immediately after startup. I had chalked it up to the timing chain hydraulic tensioners and the TSB that describes that noise, but as the sound continued to get worse and more annoying, I pushed my dealer harder to find a solution.
They heard the sound once on a visit about 9 months ago, but couldn't reporduce it, so they did nothing. The next time I had it in, they said they never heard it. Finally I pushed them to get Audi involved. The service manager contacted Audi's regional tech rep and set up an appointment for him to look at my car.
I was there with them when the service manager, the dealer's best tech, and the Audi regional tech rep started the car to listen for the noise. Luckily, the noise happened that time and the tech rep immediately said that the noise is coming from the intake manifold. This was the first time I was outside the car listening when someone else started it, so it was pretty clear to me, also, that the noise had a hollow, almost "plastic" echo that clearly was coming from the plastic manifold housing.
It turns out that the sound is the flap inside the manifold that alters the runner length to flatten the engine's torque curve. For some reason the flap is slapping open and shut a couple times when it shouldn't. They replaced the vacuum piston that contols the flap, but that didn't solve the problem. They measured the vacuum and that is fine, too. The next step is to replace the entire manifold housing with flap mechanism. I'm waiting to hear by the end of the week if that has solved the problem. Keep your fingers crossed for me.
I'll post the results next week.
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