Sensor problem?
 

Have a '04 Grand Marquis, when starting a cold engine the RPMs go through the roof, becoming normal within a few seconds however. The colder the air temp, the worse it is. Since revving a cold engine is harmful anyway, I need to get this fixed. Is it something that only needs cleaned that is relatively simple, or is it, as one mechanic advised me (without seeing the car), the carb will have to be removed, cleaned, etc.? Many thanks! ;)

Does the rpms go down by itself or when you tap the accelerator?

Sensor?
 

RPMS drop w/o tapping accelerator.

Sounds like a vacumn activated choke//high idle may be set too high when cold. This mechanism should have some way of adjusting the cold idle speed with a set screw. The choke pull-off system should also have an electrically operated pull-off spring inside a black round plastic device mounted besides the mechanical/vacumn pull-off system and connected to it via a linking rod.

This electric choke pull-off can be adjusted by loosening the three screws on the device's cover and then turning the cover to the left a 1/4 to 1/2 turn to lessen the cold starting point of the thermal spring inside. Then re-tighten the three screws.

If doing this effects the cold run conditions, the electric pull-off device may be at fault - corroded thermal spring or possibly broken or a bad connection on the 12v wire connected to the device.

As my 85 has a similar choke pull-off system (without the vacume assist) it may be slightly different so the above suggestions may not be applicable to your system but some help in narrowing down the problem.

I remember something (that you described) on one of my older Fords. But, I could not find it on my '01 Merc, maybe there is no adjustment as I was previously advised. I'll keep looking however. Many thanks!