Today the whole family took a trip outside Melbourne so I decided it was time to take the S3 for it's first 4 hr drive. I had half a tank so I topped up from the same petrol station I fill at. Took off and then next traffic light I noticed my idling was all over the shop. I stop and it goes down to 800 then starts to rise upto 2500rpm then drops again and does it again sometimes to 1500rpm and down again. It also does it if cruising in first gear around 2000rpm where it goes to 3000rpm then drops. Turned off the car and back on again and doing the same It feels all normal from second gear onwards. I finally reached our destination and after a couple of stops it was all normal. Turned the car off and on a couple of times and it's fine. I'm down to half a tank. I have stage 2 APR with full miltek exhaust and have the forge twin take. I had a look under the bonnet and everything seems fine there.
Would appreciate any suggestions to narrow my search (pcv? Bad fuel?) and whether I can still use the car as I have 400kms to get back home.