Erratic idle

Hey fellas. I'm having some problems with my 85 idling oddly. Sometimes it idles up and down it's own. Today it idled so low it killed itself. I had to pump the gas to get it started. Any ideas here? I checked for vacuum leaks and found none. Is there some sort of hot air compensator valve that maybe malfuctioning or is it simply time to rebuild the carb? It never starts the first time and usually takes three tries to for it stay running, yet I think this is unrelated to the wierd low idle and trouble starting. I changed the fuel filters out a year ago, and I suspect the fuel pump either works or not. So I'm leaning to the carb, but that's what everyone goes after first.
Thanks for any help,
D

had this on my old Si,turned out to be a leaky inlet manifold gasket.Mine ran fine on first start,soon as metal warmed it leaked causing erratic running.Worth a shot,gaskets are cheap.You can spray oil around gasket area and look for bubbles if it's the top that leaks...