I'm gonna try a set of wires.. These are probably the original with 147K , and 14 years on them.. I wrestled them around a lot getting the old plugs out too, to say the least...That's my "gut " feeling anyway..
I can re-produce the problem by pulling a plug wire off..

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89 300SEL Money Pit

92 Blown Buick Ultra Pimpmobile 220K and adding 1K per week

88 Wagoneer Slightly modified (Not for soccer moms)

04 Kia Sedona with every option... NICE