Unusual fast idle condition

[Don in VT]

Hi All,

I have a somewhat unusual fast idle situation. When I start out cold, the idle is up around 1500 rpm. When I drive a few miles and come to a complete stop the idle comes to rest at 1200 rpm. I turn off the motor and restart and the idle, after a couple of seconds, settles down to 650 to 700 rpm. I have run this scenario a number of times and it is always the same. To the best of my knowledge I have no vacuum leaks.

Any ideas ?

Thanks,

Don