My 92 400E does the same thing with dirty caps and rotors. A quick cleaning with emery cloth, then a squirt of QD electronics cleaner does the trick, they are very sensitive and seem like a catastrophic failure when bad. Replace them and keep an eye on them.

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John
2001 ML 320
1988 560 SL
2009 Toyota Tundra TRD
1992 400 E (sold '07) (bought back, '13)
2008 ML 350