To separate the idle cam from the choke

The vernier cable was commonly used in heavy truck applications,thread out to increase idle,push on button and it would release.
Hino i drove for delivering water had. It would take about 15 minutes and it would finally warm up. Set it at 600 rpms,and go inside and drink coffee. Could hear it start to rev up,had to run to idle it down,as it would go wide open if you left it too long.