high tickover

Evening ladies and gentlemen.
I have just fitted a second hand warm up reg as my 1.8 gti wouldnt tickover on its own when cold.this has now cured the fault but she will tickover at 1700 rpm for about 5mins then drops to about 12-1300 rpm.once warm this is the lowest it goes. got any clues ?

Try checking the idle screw at the back of the throttle housing, this will adjust the revs if you screw it in/out. There is a rubber washer set into the screw that gets worn, this may need replacing (?10 well spent). Also check your timing and mixture settings to get it all running smoothly.

Dan

Dano's on the button with his suggestions  

would it be cam belt or ignition timing that is the problem?