Too fast & irregular idle problem 1.8i. Airflow?

Hi All,
I've posted on the Big Block area but then say this one, so here goes again.

The car:
1.8i 1991 Mk1 cabby, LHD

The problem:
The car starts fine, idles perfectly from cold but when driving away, and lifting off the throttle to change gears the revs don't drop. Pulling up to traffic lights tends to leave the engine idling at at least 1500 rpm, even when warm. I can pull the idle down by engaging gear and letting the clutch up a little (i.e. like preparing to move off but with no additional throttle). The revs will pull back to normal idle and stay there.

It is as if the throttle is sticking open just a little or an air by pass is functioning.

Any suggestions welcome.

Thanks,
Arn
London UK

Sounds like the idle screw is loose and has unscrewed itself out. It's on top of the throttle body facing towards the rear of the car and i believe it comes in the form of a bolt. If it is too loose you can use some superglue or rubber sealant on the threads of the idle screw so it doesn't unscrew itself again.