Hi.  I have a 87 Chev Caprice with the 305 and a 4 Barrel Carb.  It has 180,000 miles on it and has been sitting for a month or two.  The motor runs pretty rough at idle...also at idle I can smell what amounts to, but stronger, exhaust inside the car and under the hood when idling.  When I take it for a test drive, under load, the smell goes away, and it runs fine.  It's just when it is idling that it operates very rough and the exhaust smell is apparent.  Also, as it idles, a carbon-like substance comes out of the tailpipe.  The cap, plugs and wires are all new and the catalytic converter is relatively new.  I've played with air and fuel mixtures on the carb and it doesn't seem to affect the way it runs. I have yet to play with the EGR at all.....What do you think?