idle problem after warmed up

is this a carby or EFI engine?

Carb

Sounds as if the auto choke is not working, you should only have to depress the throttle ones to pull the choke in and engage the fast idle, this can be complex and exact settings are required, something that a qualified mechanic need to look at and adjust or repair as required.

The fast idle does engage, once eng. Warms up to operating temp is when the idle drops so low it kills the eng. Unless I feather the gas pedal and ease the eng.to idle unassisted. But it still struggles to stay running. Accelerating through the gears and at freeway speeds it seems to be fine. Hope this helps.

You may just have to raise the base idle tents is an adjusting screw at the base of the carb at the throttle linkage, there may bec2 screws one will be for choke fast idle and the other will be base idle, the base idle screw will respond with altered revs the other if fitted there will not, mixtbute may also be out and you will have to check for vacuum leaks as well