Vauxhall Vectra power dips/hiccups

Bought car three months ago. Told that intermitant clicking noise had been checked on diagnostics and nothing found. No lights up. Car drove like a dream since buying. Now clicking stopped and sometimes when stationery cuts out. Also when driving seems to hiccup/power dips. No particular time just happens. When you put your foot down turbo kicks in lovely no prob. Still no warning lights up. Had fuel filter changed as feels as if muck in fuel. But no change.Please help. Thank you