qaz could be right. I've got a 2000 Cougar with the Duratec V6 and I had the same problem. I think the throttle hang problem and the one you're having are not quite the same thing. With throttle hang, if I'm not mistaken, there is a slight delay before the RPMs drop. But if your problem is like what I had, the RPMs will stay up for over 10 or 15 seconds - sometimes it seems like forever. I had the TPS (Throttle Position Sensor) replaced to cure an intermittent but obvious slowing down of about 5 MPH even though my foot was still on the gas. To get it back up to speed, I would have to get off the gas and get back on it. The new TPS cured this problem and also the excessively high RPM at idle.
The TPS is basically a potentiometer (variable resistor) with likely a voltage range of approximately 0 to 5 volts. As you step on the gas, the throttle cable acts on the throttle lever which in turn acts on the TPS. The TPS is the little black box attached to the entry of the throttle body opposite the throttle lever and cable. As you give it more gas, the voltage at the TPS goes up which tells the PCM (Powertrain Control Module) to richen the air/fuel mixture. As you manipulate the throttle, the resistance and therefore the voltage should change smoothly. When you have a bad TPS, the carbon trace of the potentiometer is getting worn down and no longer reports the proper voltage consistently or it will glitch, sending sudden voltage changes to the PCM. Basically, the PCM thinks you're on the gas when you're not, and vice versa. This can cause a surging sensation while at cruise, a sudden loss in power with a just as sudden return of power, bucking, etc., not to mention a racing idle. What is likely happening with the racing idle is when you're off the gas, the TPS should be reporting close to 0 volts to the PCM, but if there is a glitch in it, the PCM will still be receiving a higher voltage and therefore richening the mixture and creating a higher than normal idle.
