Problem with idle speed

Hi guys, I need some advice please.  I've an '82 1.6 GTI with an idle problem.  The engine fires up OK but instantly the rev's hit circa 3000.  Once the engine is warm (though it never really reaches the same temperature it used to reach), the rev's die to around 400.

When the engine's cold (revving at 3000) and you squeeze the tube into the Auxilary Air Valve (so restricitng air), the rev's drop down to the correct level.  But I replaced the AAV and it's made no difference.

The idle screw is currently out as far as possible (in an effort to keep the rev's higher when warm).

Any suggestions would be appreciated.

Regards