re. 5kcstq low boost, sputtering-bad temp sensor?

[Ben Swann]

More plausible is that you have a simple intake tract leak - most likely an
opening at the bottom of the Intercooler to Throttle body hose aka.
"Michelin Man hose".  You often can't see these without removing the hose
and throuroughly examining as the opening oft. occurs under a metal ring.

Don't get all complicated about the diagnosis - I always hear about clogged
cats, but have never really seen one and I have looked at a lot of them -
not saying it doesn't happen.  I have on the other hand seen/diagnosed these
symptoms.  You have an intake leak which is messing with the Idle
stabilization as well as throwing off your mixture and causing boost(metered
air) to be bled off.

Ben

[Date: Thu, 28 Apr 2005 14:29:48 -0600
From: barry at moonbeast.com
Subject: 5kcstq low boost, sputtering-bad temp sensor?
To: quattro at audifans.com
Message-ID: <1114720188.427147bce6d90 at sec.moonbeast.com>
Content-Type: text/plain; charset=ISO-8859-1

Hey gang-
It's been awhile since I've posted, hope everyone's doing well.  I seek your
wisdom once more.

My '87 5k is almost sorted out now, but I've still got some gremlins that
I'm
trying to exorcise.  Here's the major issues:

1. I'm consistently seeing low boost - in normal driving, not usually more
than
0.9bar, and not more than 1.2bar at WOT.

2. Sputtering at idle.  By messing with the idle adjust screw at the front
of
the intake manifold, I can balance it between wanting to stall and going
into
the infamous "idle bounce" mode where the engine speed rises, cuts out,
falls
then rises again (ISV and its hoses have been replaced).  The exhaust is
sputtering at idle, even though the car is smooth on acceleration and at any
road speed.

3. The water temp gauge shows full cold pretty much all the time.  It has
risen
to half scale on occasion, but unpredictably.  Most of the time it stays
pegged
on full cold, even after more than an hour at highway speeds.

4. Fuel economy is crappy- I get about 19mpg consistently, on rare occasions
topping 20.


My (admittedly inexpert) guess at this point is that the water temperature
sensor has gone bad, and the system never gets out of "cold start" mode.
It's
constantly running that intake manifold injector, which makes the system
consistently run rich, which in turn is plugging my cat.  The plugged cat is
restricting the turbocharger spool-up and making the engine sputter at
idle 'cause of the low exhaust airflow and rich mixture.

Does that sound plausible, or am I off my rocker?  Any insight/BTDT would be
greatly appreciated.

Cheers!
-Barry]