Cannot drive it yet as the clutch has gone

this isn't a problem though as the engine isn't going to be staying in the car

I just wanted the engine running OK when I sold it. (anybody want it real cheap?)
When starting from cold she fires up straight away and ticks over at about 1600 revs. After a few couple of minutes the revs drop slowly. This is where I would expect them to level off at about 900revs (ish) but they just continue going down until it stalls.
Where is the idle screw? Is it the one on the back of the throttle body?