Hi everyone, can anyone solve this one? My otherwise lovely 2003 75k estate fires up first turn of the key, but the revs then go up and down like a yo-yo between 1400 or so and 400 several times, often stalling altogether, requiring a restart. It behaves exactly like my Morris Minor (yes, I have one, please don't laugh) if I forget to pull the choke out for a cold start. I can catch it on the gas pedal and keep it running, but the owners manual says this is a bad idea. The engine management light is on, and the code reader said that the intake air temperature was too high - I can understand how this might tell the ecu to turn down the fuel supply - air less dense, therefore less fuel, revs drop and the ecu opens the throttle, and repeat. On this engine, the air temperature sensor is incorporated into the mass airflow sensor, and this was changed for a new, correct BBT item the day before the car was bought. Give the car a minute or two and it settles down and runs perfectly - until the next time you turn it off, when we get a repeat performance. I've read that if you remove or change the throttle body then it has to be "realigned" afterwards, with the old computer thingy. Does this also apply to the MAF as well, so that the ECU recognises the new one? Does the fault code have to be cleared before it behaves itself? Any ideas would be greatly appreciated.

Disconnect your maf and see if it settles.

If it does, go get a genuine one and replace it.

Thanks for the reply, Mac, I'll give it a go.  As for the MAF, BBT claim to be an OEM, the car has had this problem since I bought it, and the MAF was fitted the day before (13th July). That said, it doesn't preclude something being wrong with it.....

Vag engines are notorious for knowing a non genuine sensor has been fitted and not working properly.. be it a maf, coolant temp etc.