1996 Dodge Viper High Idle On Startup

Hoping someone has experienced this issue and can offer some help. My 1996 viper gts has 1,200 miles on it; lives in California; stored inside climate controlled shop; never been wet; had it sniffed 2 years ago; drove away; 3/4 mile down the road when I let off throttle, rpm stayed at approx 2000 for a bit, then dropped down; since then, every time it start it, it goes right to 2000- 2500 rpm; if I have it in 1st gear with brake on and force rpm down with clutch, it will come down to 800-1000 and bounce around there until I touch throttle, then up she goes. I've changed IAC and no change; I have never gotten a code yet. Little help anyone.Marlon Premou