Bill you car is blowing a bunch of accumulated crap out of the muffler. Unless it's metal, don't worry. We all produce solids at one time or another. I still think you're going to have problems with your ignition system. If the high voltage produced by the coil is weak, you will have trouble with rough idle and hard starts. The ignition control module manages dwell, timing and the like. The coil, distributor (cap), rotor and wires manage getting the spark to where it has to go. If the module is sending low voltage pulses to the coil according the ECU inputs, etc., then the coil HT voltage will be proportional to the input voltage. For your peace of mind, find a tech you feel comfortable with and get the engine scoped and see what you are actually getting from the ignition system.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.