Idle problem

I took the car cover off the stang and drove it around the block.

When I came to a stop the idle would stay at 1500-2000rpms then slowly return to normal.

I have a 650dp on a manual 347.

Any sugestions on what the problem may be?
[addsig]

Look at the throttle linkage and cable coming through the fire wall and see if they are dirty or possibley bent, some carb cleaner on the linkage may be all it needs

Throttle Return Springs can weaken over time, and they lose the ability to quickly return the throttle lever all the way to your hot idle speed setting. Check the throttle return springs, even if they aren't weak the bracket holding them may have rotated changing the tension on the springs, etc.

The secondary plate return spring is something many folks overlook. This spring is wrapped around the secondary throttle plate shaft. If it has loosened up, it does not fully close the secondaries and increases the idle by about 500 RPMs.

Simply remove the screw holding the linkage on, and pull the spring off slightly, wind it one more turn around the throttle shaft, then put it back together.

To make sure that was the problem, take the carb off the engine and inspect it yourself, you may see it not returning 100% of the time, but maybe 1 out of 10 times it does not close fully.
[addsig]