Tickover

Hi all. I have tried to lower the tick over on my golf 1800 GTi. The tick over is at 1200 when warm. I have tried the air screw on the rear of the throttle body but it's fully in. I have removed the screw and replaced to o ring but still ticking over high with it fully in. Is there anything else to check. Car runs fine apart from that.
many thanks.

The screw shouldn't be fully in if you are talking about the Idle Bypass Screw, it is usually bottomed out then back out 1/4 to 1/2 turn.

So as I am unsure of what you mean by tickover as I have a different vernacular than y'all,  please explain what you mean by tickover.

Try setting the throttle stop on the top of the throttle valve, there's usually a bit of yellow paint on the thread of the screw.
From memory - Undo the screw, put a piece of thin paper in the gap and do the screw up again until it just grabs the paper, take the paper out and do the screw up a further half turn and lock it off.

Sounds like a bit of a vacuum leak. Spray some carb cleaner on the inlet manifold gasket area and any joins in the vacuum lines.
Have yo checked the timing and mixture? Both of those can impact the idle.

Another thought, try pinching the hose to the auxiliary air valve, if that slows it down it's stuck open or lost it's power supply.

But only do that once the car is warm.

I actually have a similar issue with mine, can't get the idle down, but as it's got a mild cam in it, it doesn't idel very smoothly anyway - doesn't stall, it's just lumpy.

Thanks for the pointers guys. Will update if I manage to sort the issue.