Common problem when coming up to junctions/stopping is the ISCV (idle speed control valve mate). This won't show up on computer and it's most probably this. It's located on the inlet side on the throttle body area/section I think and is accessed from underneath the car. You can take it off, give it a bit of a clean with brake cleaner, and if you can, I've been told try to lubricate it as well to stop it drying out, with what exactly though I don't know, perhaps WD40 or spray (white) grease at a guess. It's also best to order a new gasket for it as well. About £6 delivered or a few quid if you can pop down your local Ford parts dept.