Yes, the solenoid runs up to the inlet manifold. It controls when the fuel tank vents gas into the inlet, so in theory if it or the carbon canister is dodgy, could cause an air leak. You can bin the carbon canister, block the black hose that connects to it and dangle the clear unblocked hose through a hole in the wing. See if that improves things, if not you could try and remove the solenoid completely incase it's leaking, which may cause a fault code, but could probably be defeated by a resistor in the solenoids place