hello mate worth a try, but mine was like that when i put the engine in my car, i tried all the things you have and had the same result.... then i checked all vacuum hoses i found one split and i also checked all the plugs for the sensors in, on, under and all around the inlet manifold i had left one off and one was leaking air from the centre of the inlet but i didnt even have the sensor (85+vat from ford!!) so i blocked it with a sump plug from a vauxhall i think!! after that sweet as a nut, so i highly recommend double checking all hoses and wiring as its easy to overlook or forget the small little things!!!!

also make sure there is no fuel around injectors!! good luck mate