HELP plzzzzz

hi just bought a freelander w plate 1.8 petrol had prods with missfire and juddering had service and new headgas just been done but judder remains leads look new plus the judder seems to only happen when theres a 1/4 tank of fueal remaining runs smooth on m way round town its worse any ideas what it could be cheers rich .......

You bought a Gaylander.....yes, you need help!!

found out it was ecu