have you checked the EGR , its more of an open valve on the petrols , had the same problem on a mondeo 1.8 zetec , and it was a hair line crack in the rubber air flow pipe to the egr , can cause it to run lumpy , and choke when hot , and you would normally over look it , as most egr breakdowns are on the diesels but can fail on the petrols too , also check throttle position sensor , they do get dirty an clogged up