I'd like to adjust my idle a little slower, its not bad and I can live with it, the tach reads about 1200 when warm but I think it might be reading a little high.

Can I just turn the screw down on the TB and make it slower or is this going to screw up the ECM?

The ECM controls the idle completely and permanently. Do not screw (literally) with the throttle blade adjustment. Unless you have a faulty tach (very possible), or an intake vacuum leak, you should be at the factory presets.

Get yourself a way to datalog to see if the tach and the actual idle speed corresponds.

Thanks thats what I thought.