Could also be the water pump starting to seize up, loading the engine at idle into stalling. I had this on my A4, where it would keep cutting out when cold, so had specialist check everything, they found a faulty temp sensor and replaced it, but it was still doing it. Luckily the water pump was leaking slightly so got it replaced and problem solved. They showed me the old pump and you couldn't turn it at all by hand it was so badly corroded up. Without the leak it could have cost me an engine rebuild. Thanks to Audi dealer for not replacing the pump when they did the timing belt, t*ssers.