86,
I would open up your old DME if the tabs have been disturbed and check for a chip. A performance chip could easily explain the fast-worn distributor cap and rotor (due to advanced timing) and could also account for your hunting idle. I eat distributor cap and rotors for this reason - and my idle hunts - so it's worth looking into.
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Mark Szabo
1986 911 Targa 3.2
1987 Escort 5-speed 1.9
RIP
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