My 1978' F250 with a 400ci idles roughly when cold. After 5 minutes or so it runs much smoother. Here is a video of the vacuum gauge while cold and warm. The vacuum bounces and is much lower when cold. I have checked for an intake gasket leak and found nothing. Plugs, wires, cap rotor are all in great shape. Any ideas on what to do? Thanks.

http://www.youtube.com/watch?v=r9Srr...layer_embedded

 

you might have a ring thats sticking when it cold

 

Have you done a compression test?

 

I'd try the compression test first but my gut says you have the same problem I had with one of my FEs. There is a runner in the intake manifold that carrys exhaust gases to the bottom of the carb to keep the carb from freezing in winter. A small crack can develop in this runner allowing exhaust gases to go into the intake air and create all kinds of issues. When it gets warm, the crack seals up.....for now. Mine got far worse as time went by and the engine was a pain to keep running.