Welp, my satiation with chalking it up to chasing ghosts didn’t last long - or my anxiety/boredom got to me anyway.
I have opened this can of worms again due to what I noticed the other day messing with the throttle. If I hold the RPMs at say, 1200, I can audibly hear the engine load down a bit then back up, then back down every 2-3 seconds. Similar to when the AC cycles, but not quite as pronounced, around 50-100 RPM difference, won’t ever stay steady under acceleration in park. Still have the 570-630 RPM fluctuation in park at idle that is observable on the tachometer. No engine codes, no performance or MPG differences.
A quick reminder on what’s been done - 16 plugs, 8 wires, 8 coils, 8 injectors, MAF sensor, throttle body with sensor, PCV, purge canister, air filter, up stream 02 sensor. Have done compression checks, vacuum leak checks, checked valve springs. Ran cleaners through the top and bottom end, scoped a few cylinders.
Only thing that’s a little off is I’m getting consistently negative long term fuel trims. Not too low, but around -5 to -10.
Gonna call around and see if I can find a shop or mechanic who’s really Ford versed. Out of ideas completely.
Here’s a quick vid of the Forscan data showing a few things including the RPMs at idle. YouTube video
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