PA30 Twin Commanche Idle RPM?

[Avidflyer2]

We recently acquired a new (new to us) Twin Commanche with the Lycoming IO-320 engine. The engine idle rpm is set very low - low enough that the engine may quit if the throttle is held tight against the idle stop. This setup is unique in that there is both a hard stop and a soft idle stop. The soft idle stop is where the spring cushion throttle lever idle screw contacts the fuel servo stop. So, if the throttle is brought back to the spring cushion the engine idles approx 1000 rpm, and if held hard against the hard stop the idle will drop to 600 rpm.

Question: Where does one find the idle rpm specification as it doesn't seem to be in the PA30 Service Manual? Is there a two-step idle setting, ie: adjust the spring cushion dimension first?

 

[philiplane]

 

[NorthernAviation]