Crown Vics DID have problems with excessive idling - just like any car can. In talking to mechanics, 2 basic things would happen: 1 - after idling for possibly hours, the officer would get a call, jump in, and roar off -- the engine going from idle to redline rpms instantly. That is tough on any engine. 2 - biggest reason for problems according to mechanics I talked with, was the departments trying to "save" money by not using the proper oil which I believe was supposed to be synthetic. Departments realized cheap oil would save a decent amount of money at budget time, so they went with that. The synthetic could handle the crazy idle-to-full-acceleration much better than dino oil.
So what if anything failed in the engine? Or did it just not run right? The only thing I could think of is the cam advance?