2001 F150 5.4 Lariat Idle Problem

110 K Miles. Idles At 1500 Rpm Coldstart Then Drops To 1000rpm After About 1 Minute. As I Turn My Heater Settings The Idle Surges Back Up To 1500 Rpm And Then Settles Back To 1000 Rpm, Same Thing Happens When I Put It In Gear. After The Truck Is Warmed Up The Idle Seems Ok. Whats Going On Here?