Warm up regulator

Hi, I'm pretty sure my WUR isn't functioning correctly… Can it be stripped down, cleaned and re-set?  Or do I need to buy a new unit?
 If so, where is the best place to buy one?

any advice would be appreciated!

Ta,
Ross

mk1 8v GTi 

I think there is a guide in the Haynes manual on testing the WUR so you can make sure that is your problem.
What is your problem with the car?

It idles around 500rpm when cold, and it splutters a little when I open the throttle..  It's totally fine when it's up to temperature. i.e idle is spot on and engine runs like a swiss watch.