2000 Lincoln Town Car - engine roars sometim when the engine is cold. The noise stops when the accelator is depressed. Whaat is the cause of the roar?

When the engine is cold the oil has settled in the lower engine areas. When you start the car, the oil takes a second to build pressure in parts of the engine where the oil has drained from. When you depress the accelerator you cause the oil pump to send oil to all the dry spots, thus quieting the engine noise.

It's the air idle control valve that is located on the intake. I have the same noise it's a howl or a harmonic vibration is my way of describing it . Fuel injected engines are tuned in part through the intake system, some vehicles even have air chamber boxes before the air reaches the intake. That's what that box is in the front of the engine under the engine cover at least on the ones I have worked on. I believe the light construction of this box allows it vibrate like a kazoo is what it is making the noise. There are other fo mo co vehicles that do this and at different rpms the town cars all seem to be at idle and are worse if the outside temperature is cold. Mine wont do it in the heat of summer. It is a part that costs between $35 and well over $100 if you don't mind throwing your money away. It can be replaced in less than an hour with a bit of a mechanical aptitude or pay the man either way it beats the looks you get at red lights when its cold outside.