I have a 2000 Focus. It has been making a roaring sound on starting for about a year which disappears upon engine warming. Mechanics have not been able to diagnose the problem. Sound suddenly became worse and engine became very rough and could not maintain idle. Anyone with any ideas on what is going on?

 

have the checked the starter! if the starter motor spline is not retracting completely after starting the car it can grind with the flywheel making and awful sound!
also have them check the EGR valve, and all the sensors!

 

I am a Ford Certified Tech from Canada, and I had one last week with that same concern. I found it was a faulty a/c clutch. It may not be the same concern. If it happens again switch the a/c on or off and see if the noise changes. If it does, you have pin pointed the problum.