I had the same problem - here is some advice I got that may be useful to
you.

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It is always advisable to change the ignition coil when replacing a module
on an
HEI system. Usually the primary of the coil intermittantly shorts out
causing
damage to the module. Another possibility is your pickup coil. Every time
the
vacuum advance pulls in or releases, the pickup coil leads flex. There is
just
so much flexing a 29 year old pair of wires can take, until the strands give
out. Disconnect the pickup coil, and then put an ohm meter across the pickup
coil leads. Connect a piece of vacuum hose to the vacuum advance and apply
vacuum to the hose. This will make the coil rotate. Watch for any
fluctuation in
the ohm meter indicating broken wires. By doing this, you will also find out
if
your vacuum advance is working.

The module is probably the most often blamed, but seldom the culprit.  All
of the failed hei modules I've seen , and I've seen a lot (was a lic tech
working in a busy shop in the 70's and 80's) all acted the same way.  They
always totally failed and engine quit.  Intermittent problems and rough
running were never found to be traced to a module.  Unlike others in this
post, i had never run across one that was toasted due to a bad coil.  I've
heard techs blame the coil when they had a second module fail in a short
time, but I think ultimately the failure was traced to absence of heat sink
grease in installation.  Shorted coils usually manifest themselves elsewhere
before they would ever burn a module, low secondary voltage resulting in
misfire under load etc.

Broken/breaking wires on the pick-ip coil was a high probability for this
kind of problem.  Also, look for a burn mark in the underside centre of the
rotor.  If you have a plug(s) or plug wire(s) with high resistance the high
secondary voltage will seek out it's easiest path to ground, often burning a
hole through the centre of the rotor and grounding to the dist shaft.  If
you find burning in this spot don't stop there.  Now find the cause of the
high secondary resistance, check all the plugs and wires.
In my opinion, not likely the coil, but it is possible.  Running it on an
old scope and pulling a plug wire off while running will show max coil
output.  If it's within spec keep looking, but again, yank on the pick-up
wires first.

No on the egr.  Failed and stuck  open would give you an extremely rough
idle and would smooth out at higher rpm.  Failed closed and not opening may
not even be noticeable, but can give you ignition "pinging".  If you had
previously had to retard the timing from factory settings to get rid of the
ping it may be because of the egr not functioning.  Not as prevelant on GM
vehicle, but Ford v8's would ping like crazy when the egr quit functioning.
A good working egr system allows you to run timing advanced quite a bit,
increasing power and decreasing fuel consumption.

If the pick-up is determinded to be the problem, the dist must be removed
and disassembled to replace it.  Service all mech advance items and check
the vacuum advance for proper function.  I would also check cap, rotor,
plugs and wires while I was at it, good time to do the whole tuneup thing.
Good Luck,
Steve G.