hi i have a octavia ambient tdi on a 2001 plate im just wondering how you adjust the idle speed as mine seems to be running at 900rpm which i feel is to fast and would like to slow it down slightly can anyone tell me where i adjust it manually thanks

Id very much doubt if you can alter this. You need to look elsewhere for the issue at perished rubber pipes etc as sounds like you have some sort of air leak.

You can adjust it on the 1.8t engines with vagcom, but I'm not sure about the TDIs.

Have a look for 'Idle Speed Adaptation'.

You can adjust TDI idle using Vagcom, but 900rpm is the correct idle speed on a TDI.