[Paulporsche]

There are a lot of possibilities here. When did this condition start? What was the car like before?

Turning the idle speed screw clockwise lowers the speed. It shouldn't be all the way in however. Can you back it out somewhat to achieve a happy medium?

Have you checked for air leaks? Have you checked the operation of your decel valve? Is your distributor operating freely?

Have you checked your CO%? How about your control pressures?

I would first try resetting your idle speed and seeing what happens. It's also possible your mixture is slightly lean.

Let us know what happens when you back the idle screw out a little, say in 1/4 turn increments.