RPM Based Vibration Engine or Torque Converter/Flexplate?
I have a 2000 Mustang 3.8 auto with 112K miles. I bought this car last year off the original owner and have been dealing with an engine/drivetrain? vibration ever since. To date, I've replaced:
-battery & terminals
-DPFE + EGR valve (car had CEL when purchased for P0401/402 codes)
-Harmonic balancer(no change)
-Fuel pump assy (had hard start condition in the mornings, had to cycle key to build pressure) starts up fine now
-***Trans fluid changed shortly after purchase at 103k, car appeared to have original fill, fluid was dark there was good amount of sediment bottom of pan but no chunks. Magnet had nice caked on goop.
-Filled with Castrol Mercon V after draining TC and pan.
What I experience seems to be a shudder like vibration which is RPM based from about 1200 RPM to 2000 RPM. I can replicate this sitting still in P or N. I can also replicate it to an extent if I hold gears - 1st, 2nd, 3rd, etc.
It is most pronounced in 3rd gear if I switch O/D off and cruise around 35-45MPH. It will shudder excessively here, on the throttle, cruise, AND coast down.
It is also felt in O/D on the highway under light throttle and steadY cruise around 55-70MPH.
Trans shifts fine otherwise, no slippage. Does this sound like a TC issue or maybe even flexplate issue? I have tried the brake tap test and there is no change in behavior. Would this completely eliminate the TC out of the equation?
Sorry for long post, and thanks for any help!