[V6-12v] V6-12v Digest, Vol 68, Issue 3

Thomas G. Leppke-Hennig printhead at usinternet.com
Wed Nov 18 14:27:06 PST 2009

> Message: 1
> Date: Wed, 18 Nov 2009 06:40:28 -0800 (PST)
> From: David Torrey <davidtorrey2004 at yahoo.com>
> Subject: [V6-12v] Rough Idle
> To: V6 List <V6-12V at Audifans.Com>
> Message-ID: <370578.30274.qm at web55301.mail.re4.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> Well, I replaced all spark plug wires and the rough idle persists (wires
> had 180K miles on them).? Plugs are new. I checked vacuum connections and
> can't find any issues.? I have noticed that after the car sits for 8 hours
> there is no vacuum assist for the brakes until the engine runs for about
> 30 seconds.? Not sure if this maybe related?? Possibly check valve faulty
> in the vacuum line going to the brake booster? Could it be fuel injector
> seals leaking air or MAF sensor?? Any experiences appreciated.
> David

Rough idle is not always easy to track down. The exhaust gas recirculation
valve (EGR) is a prime candidate for causing rough idle. Follow the manual
for how to test. The general technique is to remove its vacuum signal
hose, apply a vacuum to that while the car is at idle, and the idle should
get really bad or the engine should even 'die'. The reason is, is that the
valve looks like a really bad vacuum leak when open, thus the reason why
the car doesn't open it until high throttle settings and a warm engine.
Unfortunately, it isn't too easy to get to. Fortunately, there are about
10 other vacuum lines you can check for leaks while you dig into it that

There are so many other things that it could be. Bad injector, bad
connection to an injector, bad fuel injector seals, busted valve spring,
bad o2 sensors, bad fuel pressure regulator, bad plug wire, bad plug (they
are new, but that doesn't always mean anything) bad coil. Some of these
are quite far-fetched, I'm just listing them.

The injector are held in only by the fact that it is captivated by the
fuel rail and the head, so you can twist each injector a few degrees to
see how the seals feel. They typically aren't troublesome. If you do this
while running, you could possibly find a leak by perceiving a change in
idle as you rotate them.

The brake vacuum assist leak down is only a problem if it leaks down in a
minute or two. Over-night...forgetaboutit. Unhook it and plug the manifold
port if you really want to eliminate it.

Tom LH
1995 90q

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