Right, it's silly o'clock in the morning and I've got to rack my brains but here goes.
Get the bonnet up and sit in the car with the window open and listening carefully. Put the car in neutral (neutral, remember, not park - never ever rev a CVT in park, you'll burn the clutch out in minutes) and slowly increase the revs to approx 2-2500 rpm. You should hear a pronounced click from the tachometric relay in the 4-way valve. If that valve clicks then fine, if not then you may need a new tachometric relay.
Pull off one tee-piece that holds the two of the thinner pipes that come off the 4-way valve and carefully blow down it. You should be able to get air down them and then it should blow back at you when you let go. Bit like blowing up a balloon. If its too hard then take one pipe off the tee piece and then repeat with the other side. Repeat with the two thicker ones.
To do the rest of the tests you'll need an assistant. Pull off the tee-piece that leads to the thicker pipes with the engine running and the car in neutral. Verify that there is no vacuum coming from the valve. Then get the assistant to press the brakes hard. There should be a click and you should feel vacuum. The engine may want to cut out because you're introducing an air leak by pulling off that pipe...if so don't worry about it, just get the assistant to let go quickly and the engine will recover
Then release the brake, and switch on the low gear hold switch and verify the same thing happens.
Then pull the thinner pipes now and get your assistant to do the revs test. There should be no vacuum at idle. Sit in neutral and raise the revs up until the valve clicks and hold them there. There should be a vacuum felt there.
Erm I think that's it...if you get any trouble let us know. I've deliberately not put any causes down because there are so many of them and I want you to come back to us with what you've found and then we can work it out clearly.
Hope that helps.