You may have forgotten to fit the earth wire to the back of the manifold. I fitted mine to the throttlebody as it was easier. You need to use gasket silicone because the standard metal gaskets are crap, even new ones. The hissing sound.is the idle valve opening when you turn off the ignition, its the hole inside the throttle body but.thats a good sound cause at least u know it works. Use the factory airbox cone filters suck. Dont forget the air temp probe!! Nice car mate I like the dark alloys on it.