I've recently been recommended to switch from regular 91 unleaded to 95, which I have done (hurting a bit on the price rise) I worked out just before the switch I was getting a bit under 15 litres per 100kms, highway driving which I think isn't too bad. I haven't done a comparative amount of highway driving since then to compare the consumption. However, it might just be my imagination or the increasing cold weather, but I get the feeling since I started using the higher octane fuel, my engine has been popping and spluttering and farting a bit more often. It doesn't do it much, but it's often enough to take notice of, and while it has always done it, I get the feeling it's slightly more often than usual. It tends to happen at the usual times - going up hills or on cold mornings etc. I know my engine isn't tuned to perfection at the moment and needs some degree of attention, for the record. Is this natural and just a result of needing to run on the new fuel for a bit to "flush the engine" through so to speak? Or could something else be going on?