OT-Digifant Jetta Question

[rfkellner at snet.net (Rick Kellner)]

Chris, I am going to answer the questions in reverse order.  The quality
of the warm idle is perfect.  Next, I also believe that this problem has
been there a while however; it had been masked by a temperamental idle
stabilizer valve which would tend to keep the idle high.  I replaced the
valve (this summer) and, as I mentioned now idles perfectly.  Also, this
problem is only noticeable when you accelerate quickly; it is nice and
smooth during normal acceleration.  
I have been reading about the mass air sensor and it also describes the
switches (WOT and closed throttle (CT)).  One of the tasks of the CT
switch is to signal the computer and changes pulse time to aid in, as
the manual describes it, 'drive off'.  Are these the two switches you
are referring to? 

Finally, I want to add that this car is an automatic which, in a way
makes it more noticeable.  Also, I am driving it for the winter but it
is normally driven by someone else.

Thanks, Rick Kellner.



-----Original Message-----
From: scirocco-l-bounces@scirocco.org
[mailto:scirocco-l-bounces@scirocco.org] On Behalf Of Cris Carpenter
Sent: Sunday, February 08, 2004 3:29 PM
To: scirocco-l@scirocco.org
Subject: RE: OT-Digifant Jetta Question

Digifant is a funny animal compared to CIS and can be affected in 
surprising ways by many subtle things. When I was working on these cars
at 
the dealer, we would often look at things like the throttle valve
switches 
(there are 2), body to motor grounds (not the one from the battery), 
crankcase air leaks (like the valve cover grommet for the PCV system and

the oil dipstick guide), coolant temp sensor, and even oxygen sensor.
Once 
in a blue moon we'd find a problem with an air flow sensor, but that is
way 
less common than many believe. And those things I've listed above I
would 
look at only after being sure that the basics of timing and idle are set

correctly (by the book). What is the quality of the warm idle like now
(is 
it smooth and steady at 820-850 RPM)? Another potentially important 
question would be if it was fine for a long time before and then all of
a 
sudden started doing this. If it has been like this as long as you've
known 
the car, you may want to start with the basics before looking at sensors

and stuff. Otherwise you'd end up chasing your tail.
Cris

--- David Utley <mr.utility@highstream.net> wrote:
 > Digifant cars use a Mass Air flow meter that delivers info to the
computer
 > via a copper contact that slides up and down a path of carbon on a
circuit
 > board...  As the unit gets older, the path gets more and more worn
over
 > time, esp where there is the most wear...  Between idle and 2500 rpm
is the
 > most common area of these to begin to give the computer erratic
 > information....  What has most likely happened is the copper foot has
worn
 > through the circuit board at certain points, esp at the speeds you
 > mentioned...  I would take the thing off, and put a digital
mulitmeter to it
 > and see if it gave you a clean, consistent and gradual ohm change
from rest
 > position to open throttle position...  If not, it is most definitely
your
 > problem.  If so, then look elsewhere for the culprit...
 >
 > HTH
 >
 > David
 >
 > -----Original Message-----
 > From: scirocco-l-bounces@scirocco.org
 > [mailto:scirocco-l-bounces@scirocco.org]On Behalf Of Rick Kellner
 > Sent: Saturday, February 07, 2004 11:54 AM
 > To: 'scirocco list'
 > Subject: OT-Digifant Jetta Question
 >
 > My DD, a 91 Jetta 1.8l Digifant, has an annoying running problem.  It
 > will stumble or stutter at low RPM when you first give it some gas.
 > Basically, if the car is idling and you give it a quick tap on the
 > accelerator, it will run rough and stumble between 1k and 2k rpms.
It
 > acts like a carbureted car when the accelerator pump on is the way
out.
 >
 > Any ideas?
 >
 > Thanks, Rick K. 


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