[s-cars] 1993 S4 miss firing

[Kevin Barnett]

It's contagious.

I have the stuttering (shuddering) above 3000 rpm, but
not the sharp cutout at lower revs.

Haven't found a solution yet.

So far:
Tested (with known good parts):
PSO's
Coils
Computer
MAF

Replaced:
Spark plugs
Cam position sensor (while I was doing timing belt)
By-pass valve
Oxygen Sensor

Checked:
Wiring for coils
Boost leak

Tonight, went back to basics and started all over,
replaced coil rack with previously used (supposedly,
good) rack with my spark plug boots. Pulled fuse on
computer toi reset.

Left out of neighborhood and drove easily till car
warmed up (oil and water). Came to red light. On
green, rolled onto throttle (to full throtle) in first
thru third. It was my old car again. Lifted and went
to fifth. Turned off onto back road to my neighborhood
and all was good for another mile (hammering in second
and third on curvy road). Road straighten out and
BAM!, it missed like a coil failed. Hhhmmm.

Eased off and down shifted and started accelerating
hard again in second. My missing under boost is
back....

Bad coil on two seperate coil racks?
Bad plug boot?

Thanks,
Kevin

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