I have a code of p0174 for a check engine light .what does this mean?

i have 97 ford thunderbird 6 cyl.mu service engine light soon stays on.i ahve had so many problems with this .it came on before i replaced both oxygen sensors and did a diagnostic test and he told me to put highter octane in it and some stuff for injectors and carbarator and i did but came on again and this is the code .i dont want to pay someone again if they cant tell me exactly what it is.please help me please.im a single mother and dont know much about cars myself....