How would I know if the motor mounts on my Crown Victoria are loose, because sometime after the car is running I'm hearing a strange vibrating noise coming from the engine?
If it's your motor mounts, the vibration won't stop.
You'll need to get under the car and take a look. The engine mounts are pretty easy to see - they'll have cracks through them. The Left one will be cracked and the right one will be squished. Use a pry bar and a flashlight and wedge between the Trans pan and the Cross-member while looking at the trans mount. Give the trans a lift and you can see the mount separate. We've been changing a lot of motor and trans mounts on our fleet of Crown Vic Police Interceptors. Not an unusual problem. Yes it will cause a vibration at Idle and yes, it can and will change as the Power train shifts position.
Search Ford Crown Victoria Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Crown Victoria Experts