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Intermittant vibration in a 1998 Crown Vic

About 2 yrs ago there was a slight vibration in the car, it would happen every couple of months and last for about 5 seconds. It has gotten progressively worse and now happens quite often. There is no pattern as to when it will happen, when I first start the car, in park, neutral or driving. The vibration is the same at hwy speeds as it is at idle. I only have 111,000 miles on the car. I have been told it’s anything from the torque convertor/transmission to the IMRC. Can anyone point me in the right direction?

could it be as simple as a clogged fuel filter? or failing fuel pump?

I don’t think you have an IMRC. Plugs or a coil failing would be my guess.

Does the CEL (Check Engine Light) ever come on? Is there a loss of engine power when this happens? Will it happen when in Park and does the frequency of the vibration change with engine speed? Or is the vibration at a constant level not dependent on engine speed?

Since it happens idling in neutral, you can rule out everything on the output side of the transmission. That narrows it down quite a bit. First, bring all the routine engine and transmission maintenance up to date. Second, check for any diagnostic trouble codes. If none found, and the engine seems to be performing ok, no noticeable misses, same acceleration as ever, same mpg as ever, I’d suspect in this order …

  • Motor/transmission mounts
  • Torque converter
  • Intermediate shaft (if you have one)