I've successfully stopped the excessive engine vibration and the consequential intermittent rattle that goes with it, at idle with the
engine hot,
in drive and at a
complete stop. Any other circumstances and it was not present.
To do so, I cleaned the throttle body/plate, the idle air intake port, and, just for good measure, the IAT sensor and MAF sensor. Not sure if it was the secondary clean of the idle air intake port or the sensors, as there wasn't much difference with the throttle body/plate and initial idle air intake port cleaning, but it purred happily thereafter under the same circumstances.
Initially, I thought the 5-year-old battery might be putting excessive load on the alternator and/or doing a bad job of assisting/regulating, but swapping in a new battery made little difference. Old battery passed a rather long load test with my battery tester too, so I'm leaving it alone until it shows real signs of being an issue. That and I have not yet decided if I need something other than the standard starter battery for ecomodding purposes yet.
Discovered that unplugging the alternator (voltage sensor wires and field voltage and all that) took a fair bit of load off of the engine at idle. And it doesn't appear to self-excite, even at higher RPMs, so it should be really easy to disable the alternator on demand...no big contactor or such necessary.
Test ride after all was said and done, and she was still purring smoothly at idle, and neither disconnecting the alt nor temporarily removing the intake pipe (thereby circumventing the MAF sensor) set off the CEL(though I bet it would have after a while), which was a bit unexpected.
Ahh well. issue solved. Time to go order some more LED bulbs and ponder the alternator...
