Secondary Air Pump & Throttle Body
I repaired the secondary air pump on my Leon
Cupra because it was too loud and having my car sound like a hoover is not cool.
This is before the repair - notice some of the rivets have degraded and the air gaps around the edge where the air is being sucked in.
Here's the air pump repaired - I followed guides found on forums. This is a great
shop for getting the parts -
http://www.westfieldfasteners.co.uk/
Now it can't even heard.
I also cleaned out the throttle body - I followed this one of many good guides
http://hubpages.com/hub/How-To-clean-your-Throttle-Body-VWAudi-DIY#
Mine was filthy, probably the first time it's ever been done. When I turned the ignition on I could hear the throttle body going through some sort of process, that high pitched noise, possibly aligning? I also used vag-com to align the throttle body, which was a shorter process and also made a different sound. So perhaps it's best to use vag-com to re-align.
My Leon has been having some hesitation under acceleration, around 2000rpm, low revs, between gear changes, it's like hitting the brakes. It's temperamental, but often enough to annoy me. I've replaced the MAF, N75, no vac or boost leaks, no errors. I've removed the diverter/dump valve and the diaphragm is still good - also it's the uprated version ending in 710N. Perhaps it's on its way out, a bit slow to respond - it's been on the car since new, so 12yrs/55k miles.