i had very similar problem and it would idle like crap awhile back. r&r the fuel rail and put blue shop towels below the injectors and turned the key on and off several time. low and behold two injectors were leaking fuel. i bought a remaned set of 19# ford mustang injectors. been very happy ever since.shows starting off at .445 then slowly drops down to .000 when warm. So I am thinking possibly cloged injector.