Hello, Peter!
As
Дэн4ик said, you should take off and check out your compressor for a sealing ring on its piston. Its very popular reason.
Also check out topic - the hyperlink in upper message - all thoughts about air suspension problems in one place.
There are 2 ways to solve (most cases) this problem. First, is to replace compressor with the new one. Its exprensive way. And, the second way (cheaper) - is to replace sealing ring with a repair kit. You can find it on AliEpress or, maybe even on Ebay...
Part number of Touareg I Air Compress Repair kit (sealing ring with parts) is... HERRMAN - HR7L0698030. It helps me. The cheapest way. And also you can you VAG (WABCO) repir kit - 100698010A part number.
Topics
http://www.touareg-club.net/forum/showthread.php?t=8548 and
http://www.touareg-club.net/forum/sh...ad.php?t=93287 - you should also replace air compressors relay (under plastic panel above drivers legs - there are some relays) and its orange 40A fuse (under drivers seat) - it should be replaced every 4-5 years of car ownership. Also, better to replace or even dry - air compressors desiccant - plastic granules.
After replacement - air suspension needs to be adapted with VCDS or VAS PC or ODIS or matching VAG diagnosing tool.
https://www.youtube.com/results?sear...одвески+туарег
https://www.youtube.com/results?sear...одвески+туарег
If you need other help with searching places of replaceble parts or part numbers (will need VIN) - "send letters in small handwriting" - we`ll help as soon as it possible.
Оффтопик
P.s. please, say Hello to Mr. Tr., we miss him so much. Specially radio operator Katrin and her son.