there isn't an ISV on a G40. It's just an auxiliary air valve. It just opens up when cold and closes when as it warms up. The wiring to it is just for it's internal heater. So it wont flutter open & shut, it just gradually closes. It can cause problems if it's gunked up and stuck open or shut. Removing it and soaking it in petrol for a while will normally help.
You should leave the pipes connected, if you've disconnected one you've introduced a vacuum leak so it'll not run right.