High tickover. 1971 3.5 M116 Mercedes

[W109Driver]

In neutral and park.
Tick over is at about 1200rpm.
I've checked timing and tried winding in air idle screw.
1200 is as low as i can get it.
If I squeeze hose from idle valve.
Revs drop but still ticks over.
Does this mean itd getting air from a vacuum leak?
Ive had a really good look but can't see anything.
Any other ideas?