recently bought a fabia2 1.2htp fantastic car except no warning light on dash and had 2 mechanics take a look using there diagnostic machine and cant find a fault.but here is the problem, when i come to a stand still the revs go from 800 rpm down to 500-600 rpm then back up and it will go up and down until i apply a little accelerator then it stops,sometimes it wont do it one day and then it will do it 3 or 4 times in a one mile run it also does it when the engine is cold and hot but more when hot i would say.somebody has told me to take it to a skoda dealership and let them stick it on there diagnostic computer and others say i would be wasting £80 as it will sill say there is no fault till the ecu light comes on dash.it has 3months warranty with asecond hand dealer so it is more for peace of mind than anything else,has anyone else experienced something similar and what was it.any advice would be appreciated.

I had the same with my '06 1.2 Fabia MK1, but it sorted out by itself after some time passed. In my case that weird behaviour was happening when there was a lot of moisture in the air e.g. after rainfall.

When i was looking for an answer in the WWW there were some people saying that it could be the pre-catalyst or faylty lambda sensor, something that I don't believe since the warning light should appear.