Hi, I've got a 2005 GTI and over the last month or two its developed an issue where the fan will run hard like the A/C is on even when the engine is cold. When the car is up to temperature and the fan kicks in hard the engine revs rise slightly, perhaps from 800-1000 at idle then drop down again when the fan goes off making it feel lumpy.
I initially replaced the PCV when it first started thinking it was the A/C making the fan noise and the revs fluctuating were down to that.
When that didn't help and i found it did it even when the climate was off I took it to a garage and the OBD flagged a temp sensor which was replaced- but it hasn't stopped the issue at all? It doesn't happen with every journey, out of three last week for instance it only did for one spinning the fan as soon as i started up (when it was -2 outside!).
Any idea what it is- the fan assembly itself? (I suspect the smaller of the two may not be working but not 100% sure)
