Vibration when idling in neutral?

Tiny
WOLFSHEPHERD
  • MEMBER
  • 1997 LINCOLN MARK VIII
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,650 MILES
Slight vibration when idling in neutral, more heavier when in drive or reverse. Sometimes slight, other times more intense--intensity is intermittent.

I'm not delusional, it's close to a 30 years old. I've owned it for 9 years and put 120k on it myself and am fanatical OCD when it comes to its care and maintenance. The engine is very strong--smooth running. Very recent plug replacement, old plugs showed no oil burn, though thought they looked a little lean.

Smoke tested -- negative leaks
Standard motor mount test indicates mounts are good, though, honestly, I can't but think it's the mounts (hydraulic) even though they passed the rev-on-brake test.
Recent fuel pump replaced.
Recent (1 year) harmonic balancer replaced
Power steering pump solid (relatively new), not a whisper of noise, no issues.
Very recent belt pully and belt tensioner replaced.

A lotta smart people scratching their heads.

Though have yet to get a full OBD2 diagnostic scan.
Ideas?
Thursday, April 2nd, 2026 AT 4:41 PM

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