Recurring intake air sensor code on '07 B6 TDi 170bhp

[potatan]

Hi,

My engine light came on - local mechanic diagnosed it as an Intake Air Sensor fault. He cleaned it all up and reset the code but it returned within about 10 miles. I took it back to him and he replaced the actual sensor, reset the code again. It came back again this time after about 40 miles and a couple of journeys.

I haven't actually taken it back to him yet (it's Sunday) but the symptoms are the same so I'm guessing the code will indicate the same fault. As for symptoms, the car feels underpowered, misfiring on acceleration, hunting around for gears (it's a DSG auto model). Also, after the first time, I took the car out and it was warming up nicely travelling along a dual carriageway and the temperature was rising but then started to fall, even though i was at a constant 80 mph-ish. (Normally the temperature goes up perfetly linearly till it hits the dead centre of the gauge and stops there at bang-on 12 o'clock position)

Both times when he has returned the car it has run beautifully until the light came on again. So I have some questions:

1. Will a VAG dealer (or Halfords autcentre etc.) be able to find out the code for me, or will they charge? I think I know the answer to this... (my mechanic may possibly not have access to the latest diagnostic equipment for example)

2. Could something further down the intake "chain" be affecting the intake air sensor in this way?

3. Any other ideas?

I trust my mechanic, but in this instance I wonder if something is being either misread or misinterpreted, or just missed.

Thanks in advance