At cold Idle its sounds like a Jet engine

[stewie Griffin]

When we start our Oct in the morning it sounds like a jet on idle. Not unpleasent but its either blowing out or sucking in air. The car is std under the bonnet altho it did once have a carbon induction system. any ideas, is a hose split airbox not fitted properly?

[gac]

Petrol vRS? Probably the secondary air intake, it's a common failure on the AUQ and similar 1.8T engines. If there's nothing on here about it, have a gander at the Leon Mk1 forum on seatcupra.net, there's loads of advice on how to either remove and repair it (the rivets fail meaning it lets air through the casing and/or rattles like hell, replacing the rivets with bolts tightens everything up) or remove it altogether.

[RobClubley]

Sounds like the secondary air injection pump. Does it stop after about 90 seconds?

[KenONeill]

3rd vote for the secondary air pump; it's that common of an issue.

[pauldazzle]

There's a secondary air pump repair guide on uk-mkivs.net.

[amh]

Is this a basey sound you hear when cold?

[stewie Griffin]

Cheers fellas, I will look at this when I can in the meanwhile will it affect the mot emissions?

[RobClubley]

No - all it does is help the CAT to warm up quicker for California emissions laws!

So as long as you're more than five minutes' drive from the MOT centre you'll be fine