Idle problem on 1996 Mercedes-Benz SL600

I received the car with an empty tank of gas.I filled it up with 93 octane & a bottle of Lucas engine treatment.I then drove it to a laser wash.The vehicle performed great until I got home & placed the car in park.The tach started moving from 650 rpm's to app. 1300rpm's all on its own.It will only do this once the car is at normal operating temps.HELP!

Asked by for the 1996 Mercedes-Benz SL600
i suggest you clean iac motor and recheck again