What is up with A4 check engine lights?

[Wylie Bean]

Tyson,
Having owned a 99.5 A4 1.8T for the better part of 7 years until this past
Nov, I can tell you that usually it's a vacuum leak.  At one point it was
caused by the fabric hose that runs to the front of the intake manifold from
the bypass valve, the other 3 times it was due to dry-rotted check valves in
the vacuum system.  They're cheap, and easy to fix, and you can almost hear
them leaking.  On the 1.8T there were 3 of them which I replaced over the 
course of ownership.
Not sure how the 2.8 measures up in this arena, but it's worth an otherwise 
a simple hook-up to VAG-COM or the dealer's actual computer to reveal the 
issue fairly quickly.

Hope that helps.

Wylie Bean
TheRingmeister at triad.rr.com
90 Cq
92 urS4
01 allroad quattro


Message: 4
Date: Wed, 21 Feb 2007 11:16:24 -0800
From: "Tigran Varosyan" <tigran at tigran.com>
Subject: What is up with A4 check engine lights?
To: <quattro at audifans.com>
Message-ID: <088b01c755ec$c79df850$0411030a at tyson>
Content-Type: text/plain; charset="us-ascii"

Hi Guys,

I have been in the market for a 96-99 2.8L A4 for the past few weeks. Have
called quite a few of the ads in my area (seattle) and it seems like every
other car has a check engine light that will not go away. WTF is up with
that? Usually, that is some emission control BS - O2 sensors or EGR - all of
that garbage is dealer-only and will run $1-2k to fix... What I am wondering
is why are these problems so common on these cars?