Sometimes when I turn my engine on in my 2000 GT 5-speed, my rpms will go up a bit and drop to 0, consequently stalling the engine. I always have the clutch depressed all the way. I'm thinking I need to tune my car (spark plugs, etc) but I'm not sure if that's the reason for it shutting off. When I rev the engine during startup, the rpms go to 800 at idle and it works fine. I haven't replaced my spark plugs yet...

 

It's not the spark plugs it's the IAC valve. Replace it if you can, if not then take it off and clean it.