Low idle stall

I have had a problem with not being able to maintain a low idle for about a year or so. The problem seems to be getting slowly worse. Now that I have attemped to address the problem, other than moving the idle a little higher or setting the choke a little more shut, I have been unable to isolate the cause.
Heres what I have. 1966 stock 170, 2 year old remanufactured 1 barrel carb.
Idle set at a warm 600, vacuum at intake manifold reads a steady 18.5 in hg,
spraying WD40 all around carb, intake, dizzy vacuum line and wiper line does not
change the revs. Timing is set. PCV seems to work fine.
If I rev the engine and hold at high idle, No problems. If I rev the motor and release, the rpms drop so low that it stalls out. If I set the idle up as I have
been doing then it does not run smooth. Only if I rev and let off very slowly can I get back to a low idle. What are your thoughts as to where to look for a cause to this problem? Thanks in advance.

Just a shot in the dark but I would look at the idle get and see if it has some dirt in it. If you have a holly on it you can pull the front off and get a can of carb. cleaner and spray into all the openings inside and give that a try. Also look at all tha vacuum lines all the way to the wipers good luck. Bill %) ;D

Having similar problem. Idles okay when cold, runs good when driving at speed, but stalls out when idling (or foot is off the accelerator). Curious if you ever solved the problem directly. Thank.