Intlet air leak?

Hi Chaps
I've just had a look at a neighbour's 1998/9 Focus 1.6. It's running badly- the idle is a bit shaky and it's down on power. I did try to get
some fault codes out of it with VAG-COM in ODB-II mode (the only diag tool I have), but it complains and says the car isn't ODB-II compliant. Is this to be expected?
Anyway, a bit of hands-on investigation gave the sound of an air leak around the passenger end of the engine- in the vicinity of the pressure regulator. You can hear it with the engine running, and it's very clear when you turn it off- there's a hiss for a few seconds. The way the car idles and drives supports the air leak idea too.
We've wiggled hoses to no avail, and even tried the old 'spray it with wd-40' trick (no plus-gas to hand!) to see if anything changes. Nothing.
Is there a common thing to look for? I did wonder about the manifold itslef- it's plastic- but that looks a bit fiddly to get off to just look at. The inlet trunking *looks* ok too, but we didn't remove it.
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