I have a 1980 trans am with a 400 trw pistons and a comp cams 276 AH cam with a dual offenhauser intake with two edelbrock 600's.The problem is that once the weather got cold here in El Paso tx the car does not idle it surges and wont stey running I put an elecctric fuel pump and it didn't help and the car stays running only if the idle is at above 1000 rpm and I also replaced the intake gaskets and it did the same thing once i put the idle screw to a lower rpm it dies and I also put new lifters.I also noticed that there was fuel in the vacuum line to the brake booster. I would appreciate some input on peoples past experiences.  

is your fuel level in the carb too high? Sounds like too much fuel is getting by the carb.  

Not an expert, but, my engine with the 1973 400 6.6 idles at at 750 rpm.  I was just wondering if with what you have, does it have to idle 1000 rpm to idle properly anyway?  Also, I believe an automatic transmission has to idle faster, is it automatic?  Call a speed shop and ask the question.