my car intermitting run misfires and then run smooth on 2000 Lincoln Town Car

when i first start my car it will run smooth but sometime it will misfire when i first start it then as i drive it will intermitting mis fire i have replaced the plug and it does the same

Asked by for the 2000 Lincoln Town Car
I have seen the coils fail and not set a Check Engine Light, they can fail t a point where you would imaging the check engine light would have to come on but it doesn't set a misfire code or identify a failing cylinder.
1 more answer
To add to Patrick's comments, this is where a cylinder power balance test comes into play and really assists in diagnosing the problem. A high end diagnostic tool monitors the balance of cylinders verses each other so that you can see which one(s) are dropping out due to the likely coil problem.

Further support for recommending a good diagnosis. Good luck!