Hi all I have a octavia 1.9 td when it's wet my idle speed goes up by 200 not all the time but I would say about 50% of the time it goes up any one had similar problem 

so will it sit at 1,000 rpm? if so it might be doing a DPF clean, but depending on your engine / year it might not have one fitted.

 

I don't see any reason to raise the rpm in the rain and I've not heard of this being a feature of say a rain sensor.

Might be connected to damaged insulation layer of some wiring that in wet time might start behaving odd.

I've heard about some cases when in wet time it's not possible to start the car or something starts going terribly wrong etc. In this case there might be some sensor involved that sends wrong signal  - for example, the car might think that it's -30 outside and it needs higher rpm.