Whilst trying to trace the poor running of my recently acquired A4, and following the links suggested on this site (thanks guys!) I've found several mentions of the MASS AIRFLOW SENSOR. It sounds like a possible culprit and seems to be somewhere around the air outlet housings. So I had a check under the bonnet and found something not right - a pipe that connects from the back of the rocker cover to the large air outlet pipe at the back of the engine was broken in half! Obviously happened some time ago as it was partially wrapped in insulating tape, which had become caked in oil and slipped off. I took the pipe off, cleaned it and taped it back together as best I could, hoping the running would improve if the possible air leak or pressure drop was temporary fixed. Unfortunately still runs bad. Where EXACTLY is the MAF? I just had a horrible sinking feeling that it used to be housed inside that pipe and has fallen out when the tape gave way? I know that replacement MAFs are very expensive, so any advice on where it is, how to remove it and check/clean it would be much appreciated.