[boyt911sc]

Nic,

Your '75 has air pump? Do you have 3.0 liter motor in your car? I'm totally baffled by this information and interested to learn more about your car. If you could turn the idle screw several turns from either directions and don't get any idle speed change at all, I would put my money on unmetered air going into the system. A faulty (leaking) decel valve could contribute to this problem. Keep us posted.

Tony