1967 Mustang 302 motor

I am asking this question for my brother in law, He has a holley carb 670cfm street avenger on the motor, When the car is idling the rpms have to be at at least 1500 or it will stall. He has replaced all the gaskets so no vacuum leak, timing and distributor has been checked. It is not the idle screws, The ignition has been checked also, So our question is how to get the idle down without the car stalling, what could be the cause and how can we fix it?

 

More info. Are you sure there are no vacuum leaks? Spray some brake cleaner along the intake manifold gaskets when the car is idling, if the idle changes you have a vacuum leak. What's the timing at, and what's the compression ratio and what cam is being used? Also is it a manual or automatic, and if it's an automatic are you checking it in or out of gear? What power valve is in it? What's the vacuum at idle? What secondary spring is in the carb?

 

Bump

 

Does he have power brakes?,,,

Remove and plug all vacum connections on the intake and the carb, especially the power brake vac hose.

Try and run the car, if it still wont run right, I would think that you might have a carb issue. "Borrow" another carb, and see how it runs. If the car still runs bad, we are most certainly back to a vac leak again. Possibly under the manifold?