Got a 2005 a4 cabrio, again.... This one has a rough idle with the occasional yellow light. Had initially thought it was the PCV valve UFO thing next to the bulkhead. Replacing that has improved it slightly but after searching the internet most people say try and take the oil cap off when running. With the old valve I could, just. With the new one its much worse. Got a couple of spare coil packs which was a doh moment. Should I be looking for another valve or a vacuum leak?
I'd go vacuum leak, mine was horrible at idle when I had one. I thought I'd broken something but it'd just got brittle with age and cracked.