Really shouldn't be running 98ron unless it's tuned for it, the reason being is that the ignition timing on 98ron differs greatly, along with required engine compression, after continued use it could burn your valves (worst case). i experienced the same issue (only whilst turning it over), went back to 91ron not a drama after that. And Caltex is by far the WORST fuel i've put in a falcon, rough as guts like it's full of water.
But if you don't think it's a fuel issue, then maybe try looking at your throttle body/air intake, could be dirty.
|