[s-cars] 2Krpm stumble... over and over

[Vincent Frégeac]

Hi all,

I'm still stuck with the 2Krpm stumbling on my '96 S6. As of today,
changed all spark plugs, coil boots and coils. I try to comfort myself
by thinking the coils were completly rusted and would have failed soon
anyway, but I'm a bit tired to spend money on this car and get no
improvement.

Here is the problem, as detailled as possible. As the title says, the
car stumbles from 2Krpm to 2.5Krpm in first and second gear. Stumbling
disapear around 2.5Krpm if I'm light on the gas pedal but can stay up
4Krpm if I keep accelerating. Also stumbles around 1Krpm in first gear.
Barely perceptible when the engine is cold but horrible in traffic on
hot days. Stumbling is very harsh, feels more like mechanical but it's
related to the engine temperature so it seems to be ignition. More over,
when I changed the spark plugs, the stumbling improved a bit. All coils
tested with large gap sparkplugs but I haven't seen any difference in
the sparks. I changed one, moved on all position, changed two then, in a
desesperate attempt to get rid of this stumbling, changed all. All
splicing is soldered - and I do know how to solder - and protected with
heat shrink tubes.

Above 3Krpm, nothing. I can floor it, not the smallest vibration... on
good days. Idle is relatively smooth but not the best I've experienced.
Just had a dead POS channel a few days ago but I swapped wires and idle
is back to normal operation. Other phenomenon which may be related.
Sometimes, the car runs rough, with a slight vibration at all rpm except
idle whatever the acceleration. I can't say for sure it's weather
related but it seems to happen on hot and humid days. I also have
hesitations, from time to time, the kind you'd feel when a bubble goes
through the fuel line. But it's much smoother than the stumbling. All
electrical connectors have dielectric grease and doesn't show any
corrosion. Oh, and no code.

So, any clue?



Vincent.

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