Now and again while idling the revs would go up to nearly 1000 and high idle. 

Now my mechanic is saying my altanator is craping out and it's high idle is compensating for the power that it needs. 

I've never hurd audis doing this, can some one tell me if this is true thanks. 

Hello Dean,

Sounds like you need to have the alternator output checked then, to confirm or refute his diagnosis, before investigating any other possible causes. 

Kind regards,

Gareth. 

So the audi would high rev to compensate for voltage is that true 

Could be a number of issues Delano, so if your mechanic says it’s the alternator then.......

Kind regards,

Gareth. 

It could  also just be doing an engine regen to get rid of unburnt carbon. This happens now and again if you drive it very economically. Now and again you need to give it a bit of heavy right foot to clear it.