signs of a leaking gasket

I have a fe390 engine with oil between the head and intake. Now my question to you experts out there is this. With a leaking gasket would that speed up the idle speed. I thought when my car was returned to me that the car was racing at about 650 rpms. It should be at 475 rpms. I thought maybe the accerator lingage wasnt returning properly. Or the idle set screw on the carb was miss adjusted. Iam thinking its a symtom of a leaking gasket under the intake. Can you confirm and explain my theroy on that. This is a 62 tbird. Thank you Larry

Losing a bit of vacuum via an intake leak would affect your idle speed, wouldn't it? I wonder if you have an oil leak that is also sucking air?

thanks roger. I couldnt understand the faster idle. That theroy explains it all. Larry. Both corner on the rear our leaking.