It's sometimes hard to say what can be wrong without driving it....but l would start with..

check the air filter...can be dirty/blocked and need replacing
make sure all vacuum lines are attached and where they should be.

You can try just turning up the idle speed, but if it idles fine normally, and only stalls when slowing down, then l'd think it's something else.

Oh yeah prob best to adjust idle screw when hot, as this is the condition it will be in when driving (use choke when cold!)