[s-cars] '92 S4 Stumble when Cold

[Ian Duff]

My first thought was all the electrical crap in the passenger footwell,
and the potential for water to get in there. Since I thought of it too,
the real problem undoubtedly lies somewhere else.

-Ian Duff.
-----Original Message-----

From: James Murray <james.murray at ericsson.com>
Date: Monday, 20 January, 2014 at 10:21
To: "racingiron at comcast.net" <racingiron at comcast.net>, s-CAR list
<s-car-list at audifans.com>
Subject: Re: [s-cars] '92 S4 Stumble when Cold

Jeff, here's a few to check & replace:

- Check your grounds (driver & passenger footwells), there are two
grounding posts on each side.
- Check connection on your MAF
- Check your vacuum hoses to the FPR (all tight? no splits or air leaks)
- Check your connections to/from POS & coils

- Replace the ignition & fuel Thermal breakers (passenger footwell) with
blade fuses. Why? because Audi did so in the S6 (now blade fuses), and
frankly this will eliminate the guess work if you have a contact issue
within the breakers (like I did).
 
Cheers, /Jamu

________________________________________
From: s-car-list-bounces at audifans.com [s-car-list-bounces at audifans.com] on
behalf of racingiron at comcast.net [racingiron at comcast.net]
Sent: January 20, 2014 10:13 AM
To: s-car-list at audifans.com
Subject: [s-cars] '92 S4 Stumble when Cold

Now that Jeff's problem seems resolved, let's try another... This time on
my bone-stock '92 S4.

Over the past few months the car has had a split-second ignition cut-out
shortly after cold startup.  It happens within 100 yards of me pulling
away from my driveway.  Usually just one quick cut, but sometimes twice
with a few seconds between.  After that, the rest of the drive is
completely uneventful.

Now, I've had POS problems in the past, so I know what a single cylinder
failure feels like.  This is definitely NOT like that.  It's a pretty
violent jolt if I'm giving a moderate amount of torque (still relatively
small, since this is right after startup--nowhere near boost levels), but
the power comes back immediately (which probably adds to the jolt
feeling).  I've been able to glimpse the tach on a couple of occasions,
and it doesn't bounce at all.  I pulled codes a while back but got
nothing.  I'll check again to be sure.

Here's the weird part.  I confirmed this is definitely temp related during
the polar vortex two weeks ago.  Even down here in TN it got pretty cold,
with a couple of days staying in the single digits.  On those days, the
stumble didn't happen right after startup, it only appeared after several
miles of driving.  Then, it remained for much of the drive, happening
randomly several times a minute.  It's as if some component starts to fail
at a very specific temperature, but is fine above or below that.

Even more strange, after that cold snap left, the morning stumble seems
much less frequent, happening less than 50% of mornings rather than the
80% before.  So, anybody got ideas on what could cause a temp-dependent
momentary complete ignition failure?  My '93 is a running parts car now,
so I can swap most parts pretty easily, with the only know-bad component
being the FPR.

TIA,
Eric R.
'86 urq
'92 urS
'93 urS
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